(1) In word processing, any group of characters separated by spaces or punctuation on both sides. Whether it is a real word or not is unimportant to the word processor.
(2) In programming, the natural data size of a computer. The size of a word varies from one computer to another, depending on the CPU. For computers with a 16-bit CPU, a word is 16 bits (2 bytes). On large mainframes, a word can be as long as 64 bits (8 bytes).
Some computers and programming languages distinguish between shortwords and longwords. A shortword is usually 2 bytes long, while a longword is 4 bytes.
(3) When capitalized, short for Microsoft Word.