. A single unit in a device for changing radiant energy to electrical energy or for controlling current flow in a circuit. 2
. A single unit in a device whose resistance varies with radiant energy. 3
. A single unit of a battery, primary or secondary, for converting chemical energy into electrical energy. 4
. A simple unit of storage in a computer. 5
. A limited region of space. 6
. Part of a lens barrel holding one or more lenses.