Cleft sentences are grammatical constructions that break information into two clauses to provide emphasis on a particular piece of information. There are two main types: it-cleft sentences which use "it is/was" to highlight a word or phrase, and wh-cleft sentences which use "what" to focus on a word, phrase, or action. Cleft sentences allow speakers to rearrange elements in a sentence to draw attention to a specific subject, object, time, place, or other element.