Wrist rest
Alternatively referred to as a wrist pad, a wrist rest is an ergonomic padding or device designed to help provide comfort and to avoid wrist injuries when working on a computer keyboard or mouse by providing support for the wrists and keeping the hands in a more ergonomic position. Below is an example image of the Saitek Gamers' keyboard and an example of where the wrist pad is commonly located.
Also see: Carpal tunnel syndrome, Keyboard definitions, Mouse definitions