An ampersand (&), also commonly called an "and sign," is a logogram representing the conjunction "and." The symbol is a ligature of the letters in et, which is Latin for "and." Its origin is apparent in the second example in the image to the right; the first example, now more common, is a later development.
Placed at the end of a command to specify that the client started by the command should be started as a background process. The command can be typed after the command-line prompt or included in a file such as .x11start or .hpwmrc.