Definitions
1.NounAny word used as the key to a code.
2.NounAny word used in a reference work to link to other words or other information.
3.NounAny important word in a text or document, which may be linked to other words or other information, or listed in the metadata for searches to find.
4.NounA reserved word used to identify a specific command, function, etc.
5.NounAny word that occurs in a text more often than normal.
6.VerbTo tag with keywords, as for example to facilitate searching.