Office Chair Glossary: Synchro-Tilt, Lumbar, Waterfall Seat & 40 More Terms

Most office chair specifications are written for buyers who already understand them. The result is that people choose a chair by appearance and price, then discover that the mechanism they paid for is not the one their body needed. The single most useful thing a home worker can learn is the difference between a tilt that moves the seat and back together at a fixed angle and one that moves them at different rates.

This glossary defines the terms that appear on UK product pages, grouped by the part of the chair they describe. Where a term is used loosely by different manufacturers, we say so rather than pretending the industry agrees. Definitions are specification led, and we have not attached figures to any claim about comfort or performance that could not be stated as a measurement.

Key findings at a glance

• Tilt mechanism terminology is the least standardised area of chair specification and the most consequential for daily comfort.
• Synchro tilt describes a recline where the backrest and seat move at different rates, commonly around two degrees of back movement to one of seat movement.
• Lumbar support is a location, not a feature: the term is applied to fixed mouldings, height adjustable pads and dynamic tensioned systems that behave very differently.
• A waterfall seat edge is a front edge curved downwards to reduce pressure behind the knee, and it matters most for shorter users whose feet do not rest flat.
• Gas lift classification under the BIFMA and EN standards describes stroke length and load, which is why two chairs with identical seat heights can have different adjustment ranges.
• Mesh, foam and moulded foam backs are construction descriptions rather than quality indicators, and each can be executed well or badly.
• Terms such as ergonomic and orthopaedic carry no regulated definition in UK furniture retail and should be read as marketing categories.

Mechanism terms: how the chair moves

Synchro tilt. A mechanism that reclines the backrest and seat together but at different rates, so the back opens the hip angle while the seat tips only slightly. It keeps your feet on the floor and your eyes level with the screen as you lean back. This is the mechanism most people picture when they imagine a task chair reclining properly.

Knee tilt. The pivot point sits forward, near the front of the seat rather than under its centre. The front edge stays closer to its original height as you recline, which keeps the feet grounded. Common on executive chairs.

Centre tilt. The whole seat and back assembly tips around a central pivot. Simple and durable, but the front edge lifts as you lean back, which can lift the heels of shorter users.

Free float. The backrest follows the user continuously with light tension and no locking position. It suits people who move often and dislike feeling held.

Tilt tension. The adjustment, usually a knob under the seat, that sets how much effort is needed to recline. It should be matched to body weight, not set to maximum by default.

Tilt lock and multi position lock. A single lock holds the chair upright. A multi position lock holds the recline at several set angles, typically three to five.

Weight activated mechanism. Recline resistance is set automatically by the user’s weight rather than by a tension knob. Convenient, and less adjustable at the extremes of the range.

Gas lift. The pneumatic cylinder that raises and lowers the seat. Cylinders are classified by stroke length and load rating, so a chair described as having a class four gas lift is telling you about the cylinder’s specification rather than the chair’s quality.

Seat slide or seat depth adjustment. Moves the seat pan forward and back independently of the backrest so the backrest can support the lumbar spine while leaving clearance behind the knee.

Back and support terms

Lumbar support. Support shaped to the inward curve of the lower spine. The term covers fixed mouldings built into the backrest, separately adjustable pads that move up and down, depth adjustable systems that push forward, and tensioned mesh that flexes. When a listing says lumbar support, ask which of those four it means.

Adjustable lumbar. Height adjustable, depth adjustable, or both. Height adjustment matters more for tall and short users, depth adjustment matters more for people with a pronounced lower back curve.

Backrest height adjustment. Raises the whole back, and by extension the lumbar curve, to suit torso length. Distinct from lumbar pad adjustment.

Headrest. Supports the head in recline. In an upright typing posture it is rarely in contact, which is why a fixed headrest set too far forward can push the head into a chin down position.

High back, mid back and low back. Descriptions of how far the backrest rises relative to the shoulder blades. High back reaches the upper shoulders or beyond, mid back to around the shoulder blade, low back to the mid spine.

Mesh back. A tensioned fabric membrane over a frame. It distributes pressure across the frame edge rather than compressing like foam, and it allows airflow.

Moulded foam. Foam formed in a mould to a fixed shape, rather than cut from a block. It holds its profile longer than cut foam of similar density.

Cold cure foam. A foam production method producing a resilient, durable foam widely used in seating. It is a manufacturing description, not a comfort rating.

Seat terms

Waterfall seat edge. A front edge that curves downwards and away from the thigh. It reduces pressure on the underside of the thigh behind the knee, which is where circulation is most easily restricted when the feet do not sit flat on the floor.

Seat pan. The structural base of the seat beneath the upholstery.

Seat depth. Measured front to back on the sitting surface. A useful check is to leave roughly two to three finger widths between the front edge and the back of the knee.

Seat width. Measured across the widest usable part of the seat. On chairs with pronounced side bolsters, the usable width can be noticeably less than the overall width quoted.

Seat height range. The vertical travel from lowest to highest. For most UK desks, which sit at a conventional 72cm to 75cm high, a seat range of roughly 42cm to 52cm covers the majority of adults.

Seat tilt or seat angle adjustment. Tips the seat pan forward or back independently of the backrest. A slight forward tilt opens the hip angle and is favoured for detailed desk work.

Contoured seat. A seat shaped with a slight dish to locate the sitter. Helpful for stability, less forgiving if the shape does not match your build.

Arms, base and castors

Fixed arms. No adjustment. Check the height from the seat surface to the top of the arm against your desk, because fixed arms that will not slide under a desk force the chair backwards.

1D to 4D arms. A shorthand for the number of directions an armrest adjusts. Height only is 1D, height and width is 2D, adding depth makes 3D, and adding pivot or rotation makes 4D.

Cantilever arms. Arms supported from the back or side rather than rising from the seat, leaving the space below the arm open.

Loop arms. A continuous loop from the seat to the arm top, common on executive chairs.

Five star base. The standard five leg base, used because five points give a stable footprint with a lower tipping risk than four. Bases are made in nylon, glass filled nylon, aluminium and steel.

Castors. Wheels. Hard castors are intended for carpet, soft or dual wheel castors for hard floors. Fitting the wrong type is a common cause of complaints about a chair rolling away or marking a floor.

Glides. Non rolling feet fitted instead of castors, used where a chair should stay put.

Swivel. Rotation of the seat on the base, typically through a full 360 degrees.

Materials, standards and marketing language

Bonded leather, faux leather and PU. Bonded leather contains reconstituted leather fibres in a backing. Faux leather and PU are synthetic coated fabrics. None of the three behave like full grain leather over time, and all three are more sensitive to heat and direct sunlight.

Full grain and top grain leather. Full grain retains the outer hide surface. Top grain has been sanded and finished. Both are genuine leather, with different appearance and wear characteristics.

Martindale rub count. A textile abrasion test result quoted for upholstery fabrics. It describes abrasion resistance in a laboratory test and is not a general durability score.

Weight capacity. The maximum user weight the manufacturer states the chair is tested for. Treat it as a specification limit rather than a recommendation.

EN 1335. The European standard series for office work chairs, covering dimensions, safety and test methods. When a UK listing references a chair type A, B or C, it is referring to the adjustment categories within that standard.

BIFMA. The North American furniture standards body whose test methods are frequently cited on imported chairs.

Ergonomic. An unregulated descriptor in retail. Ergonomics is the practice of fitting the task to the person, so a chair can only be ergonomic in relation to a specific user and desk.

Orthopaedic and posture chair. Marketing categories with no standard definition in UK furniture retail. Neither implies medical assessment or approval.

Matching the terms to a chair that fits

The table below translates the vocabulary into the adjustment that solves each common complaint. It is a specification mapping rather than a ranking.

Common seating complaints and the chair specification that addresses each one.

Complaint	Term to look for	What it does
Pressure behind the knees	Waterfall seat edge, seat slide	Removes the hard front edge and shortens effective seat depth
Lower back aches by mid afternoon	Height adjustable lumbar	Places support at the actual curve of your spine, not an average one
Feet do not reach the floor	Lower seat height range, footrest	Restores contact so the thighs are not carrying body weight
Chair feels like it fights you when leaning back	Tilt tension adjustment	Matches recline resistance to body weight
Cannot get close enough to the desk	Height adjustable or 3D arms	Allows arms to clear the desk edge or pass beneath it
Chair rolls away on a hard floor	Soft or dual wheel castors	Increases rolling resistance and protects the floor
Shoulders creep upwards while typing	Armrest height adjustment	Supports the forearm so the shoulder can relax

What this means for UK homes

Home offices in UK houses are rarely dedicated rooms. They sit in bedroom corners, on landings and at dining tables, and that changes which specifications matter. In a shared room, a mesh back reads as lighter and takes up less visual space. Where the chair is pushed under a desk at the end of the day, arm height and overall width decide whether it actually fits.

Measure the desk before the chair. Most UK desks, including the majority of our modern computer desks UK, sit near the conventional 72cm to 75cm worktop height, and the chair has to bring you to that surface with your forearms roughly level. If your feet then lift off the floor, the answer is a footrest rather than a lower desk.

Prioritise in this order: seat height range, seat depth, lumbar position, arm adjustment, then everything else. A chair with a perfect headrest and the wrong seat depth will be uncomfortable within an hour. When we help people choose from our modern office chairs UK sale, those first three checks resolve most fit problems before style enters the conversation.

Gaming chairs follow a different design tradition, borrowed from bucket seats, with high side bolsters and a tall back. That shape suits reclined use and taller frames, and suits shorter users less well because the bolsters set the usable seat width. If you are choosing between a task chair and one of our gaming chairs UK, decide first whether you sit upright and forward or reclined, because the two shapes are optimised for opposite postures.

Finally, remember that no chair fixes a static day. Adjustment exists so that posture can change, and the mechanism terms in this glossary are all, in the end, descriptions of how easily a chair lets you move.

Methodology

This glossary was compiled by our editorial team at Furniture in Fashion from standard office seating terminology, published specification language used across the UK furniture trade, the dimensional conventions of domestic and office desks, and our own editorial assessment as a UK furniture retailer. Where terms are defined within the EN 1335 office chair standard or by BIFMA test methods, we have said so. It does not include proprietary sales data, customer data or survey fieldwork, and no laboratory testing was carried out for this report. Measurements given are standard specification ranges rather than research findings. Our full range is at Furniture in Fashion.

Citing this report

Publications, journalists and websites are welcome to quote these definitions with credit to Furniture in Fashion and a link back to us. This is an editorial glossary of trade terminology rather than a standards document, and we would ask that it is described that way. Where a term is contested within the industry, we have flagged it rather than resolved it.

Frequently asked questions

What is the difference between synchro tilt and a normal tilt?

A basic centre tilt moves the seat and back as one unit, so the front of the seat rises as you recline. Synchro tilt moves them at different rates, typically opening the backrest roughly twice as far as the seat tips, which keeps your feet on the floor and your screen in view while you lean back.

Do I need a waterfall seat edge?

It matters most if you feel pressure or numbness on the underside of your thighs, which usually means the seat is too deep, too high, or has a hard front edge. A waterfall edge relieves the pressure point, but if your feet do not reach the floor you also need a lower seat or a footrest.

Is a mesh back better than a padded back?

Neither is inherently better. Mesh distributes pressure and allows airflow, which suits warm rooms and long upright sessions. Foam offers a more enveloping feel and usually a softer contact with the shoulder blades. Both can be well or poorly made, so judge the specific chair rather than the category.

Does the term ergonomic mean anything on a UK product listing?

Not in any regulated sense. Ergonomics means fitting equipment to the person, so a chair is only ergonomic in combination with a particular user and desk. Read the adjustment list instead: seat height range, seat depth, lumbar position and arm adjustment tell you far more than the word itself.

How do I know if a chair will fit under my desk?

Measure from the floor to the underside of the desk, then compare that with the chair’s lowest arm height measured from the floor. If the arms will not pass underneath, either the arms need to be height adjustable or the chair will always sit further back than you want.