the use of hierarchies based on words rather than notations. Each topic is allocated to a group, and that group is allocated to a more general group, and so on. Searching typically involves moving from more general to more specific topics; for example, to search for information on children's birthday parties you might first select the option Celebrations, then Birthdays, then Children's parties. Category structures are fairly arbitrary and may vary widely from one site to another; on a different site you might select Catering, then Parties, then Children's parties, then Children's birthday parties, eg. By using techniques such as double posting and cross-referencing, categorised sites can provide for access from several different directions. See also automated categorisation.

a group of people or things arranged by class or category

the basic cognitive process of arranging into classes or categories

the act of distributing things into classes or categories of the same type

See Incident Categorisation.