In corpus linguistics, a collocation is a series of words or terms that co-occur more often than would be expected by chance. In phraseology, a collocation is a type of compositional phraseme, meaning that it can be understood from the words that make it up. This contrasts with an idiom, where the meaning of the whole cannot be inferred from its parts, and may be completely unrelated.

An example of a phraseological collocation is the expression strong tea. While the same meaning could be conveyed by the roughly equivalent powerful tea, this adjective does not modify tea frequently enough for English speakers to become accustomed to its co-occurrence and regard it as idiomatic or unmarked. (By way of counterexample, powerful is idiomatically preferred to strong when modifying a computer or a car.)

There are about six main types of collocations: adjective + noun, noun + noun (such as collective nouns), verb + noun, adverb + adjective, verbs + prepositional phrase (phrasal verbs), and verb + adverb.

Collocation extraction is a computational technique that finds collocations in a document or corpus, using various computational linguistics elements resembling data mining.