A 19-inch rack is a standardized frame or enclosure for mounting multiple equipment modules. Each module has a front panel that is 19 inches (482.6 mm) wide, including edges or ears that protrude on each side which allow the module to be fastened to the rack frame with screws.

Equipment designed to be placed in a rack is typically described as rack-mount, rack-mount instrument, a rack mounted system, a rack mount chassis, rack mountable, or occasionally simply shelf. The height of the electronic modules is also standardized as multiples of 1.75 inches (44.45 mm) or one rack unit or U (less commonly RU). The industry standard rack cabinet is 42U tall.