A ''hardware word'' is the group of bits normally managed by a processor. The word size is a distinguishing feature of a processor, and is typically a power-of-two multiple of eight bits (8, 16, 32, or 64 bits), although some rare or early processors used different word sizes.

The word size is usually associated with the size of general-purpose [[Register|registers]] and the amount of data read from or written to memory at one time. Most modern processors can read/write alternate word sizes (for example, a "64-bit" x86_64 system can also read/write 16 and 8 bit values to/from memory).