Phraseology is a separate branch of Linguistics which deals with a phraseological subsystem of language, with all types of set-expressions. The basic unit of phraseology is a phraseological unit. According to A. V. Koonin «a phraseological unit is a stable word-group characterized by a completely or partially transferred meaning».
Phraseology studies the following types of set-expressions: phraseological units (proper); phraseomatic units; border-line cases belonging to the mixed class.
There exist other approaches to the problem of phraseology: the semantic approach developed by academician Vinogradov; the functional approach; the contextual approach worked out by N. N. Amosova and etc.
A phraseological unit is a word-group which presents a functionally, semantically and structurally inseparable unit. Phraseological units or idioms are contrasted to free phrases.
