A word is the amount of data that a processor can fit in its general-purpose registers -- effectively the amount of data the processor can handle "at once". Programming-related questions concerning Microsoft Word should NOT use this tag - use the tag [ms-word] and/or [vba] instead. Questions on general usage of Microsoft Word are off-topic for Stack Overflow and should be asked on Super User instead.
A word is the amount of data a processor can fit into its general-purpose registers, which is a fast storage location for data or addresses of other locations in memory (e.g. other data needed for handling the current instruction).
In modern architectures, a word is typically in powers of 2. For instance, a 64-bit processor has a word size of up to 64 bits, whereas a 32-bit processor has room in its registers for up to 32 bits of data. As a counter example, the Burroughs B5000 had a word length of 48 bit.
Do not use this tag for questions about Microsoft Word or documents made with it. For these questions, use the ms-word tag, one of the version-specific word-2010, word-2007, word-2003 tags, and/or the vba tag. Questions on the general usage of Microsoft Word are off-topic for Stack Overflow and should be asked on Super User instead.
