[techspeak] A unit of memory or data equal to the amount used to represent one character; on modern architectures this is invariably 8 bits. Some older architectures used byte for quantities of 6, 7, or (especially) 9 bits, and the PDP-10 supported bytes that were actually bitfields of 1 to 36 bits! These usages are now obsolete, killed off by universal adoption of power-of-2 word sizes.
Historical note: The term was coined by Werner Buchholz in 1956 during the early design phase for the IBM Stretch computer; originally it was described as 1 to 6 bits (typical I/O equipment of the period used 6-bit chunks of information). The move to an 8-bit byte happened in late 1956, and this size was later adopted and promulgated as a standard by the System/360. The word was coined by mutating the word ‘bite’ so it would not be accidentally misspelled as bit. See also nybble.