Seat

The thing you sit on.

There are fancy seats with a gazzillion adjustments (some of which are quite nice) such as the ones from Wilderness Systems. At the other end of the spectrum are flat foam pads.

A seat should have some shape to it. If it is really flat, you will tend to sit on a couple of points on your butt and circulation will be compromised. This leads to legs and feet falling asleep. If the seat is curved to match the shape of your butt, you will have more support and will be able to sit for a longer time without discomfort.

See also: Making a Seat