Complementizer
In linguistics (especially generative grammar), a complementizer or complementiser (glossing abbreviation: comp) is a functional category (part of speech) that includes those words that can be used to turn a clause into the subject or object of a sentence. For example, the word that may be called a complementizer in English sentences like Mary believes that it is raining. The concept of complementizers is specific to certain modern grammatical theories. In traditional grammar, such words are normally considered conjunctions. The standard abbreviation for complementizer is C.