This document discusses phraseological units in English. It begins by defining phraseology as a branch of linguistics that studies phraseological units. There are various terms used to describe phraseological units such as idioms, set phrases, and phraseological units. The document then discusses criteria for identifying phraseological units, including semantic and structural criteria. It outlines three main approaches to studying phraseological units: semantic, functional, and contextual. Finally, it describes several classifications of phraseological units based on semantic, structural, and functional factors.