The term phrasal verb is commonly applied to two or three distinct but related constructions in English: a verb and a particle and/or a preposition co-occur forming a single semantic unit. This semantic unit cannot be understood based upon the meanings of the individual parts in isolation, but rather it must be taken as a whole. In other words, the meaning is non-compositional and thus unpredictable. Phrasal verbs that include a preposition are known as prepositional verbs and phrasal verbs that include a particle are also known as particle verbs. Additional alternative terms for phrasal verb are compound verb, verb-adverb combination, verb-particle construction, two-part word/verb, and three-part word/verb (depending on the number of particles), and multi-word verb.