In corpus linguistics, collocation defines a sequence of words or terms that co-occur more often than would be expected by chance. In phraseology, collocation is a sub-type of phraseme. An example of a phraseological collocation (from Michael Halliday)is the expression strong tea. While the same meaning could be conveyed by the roughly equivalent *powerful tea, this expression is considered incorrect by English speakers. Conversely, the corresponding expression for computer, powerful computers is preferred over *strong computers. Phraseological collocations should not be confused with idioms, where meaning is derived, whereas collocations are mostly compositional.

There are about six main types of collocations: adjective+noun, noun+noun, verb+noun, adverb+adjective, verbs+prepositional phrase, and verb+adverb.

Collocation extraction is a task that extracts collocations automatically from a corpus, using computational linguistics.

Collocations are in effect partly or fully fixed expressions that become establishedthrough repeated context-dependent use. Such are 'crystal clear', 'middle management', 'nuclear family', and 'cosmetic surgery' are examples of collocated pairs of words.