An indentation in an optical medium such as a CD-ROM or DVD. The laser beam is either absorbed in the pit or reflects off the non-indented areas, which are called "lands." Using various algorithms, the reflections are converted into 0 and 1 bits.
Pits and Lands
This microscopic view of a CD-ROM and DVD disc compares the track density and pits and lands, which account for 7.5 times as much data on the DVD. (Image courtesy of C-Cube Microsystems.)