COMP

In Generative syntax, COMP is an abbreviation of complementizer.

Comments
The form COMP was widely used in the classical period of Government-Binding theory in the 1980s. Since the 1990s, the simple abbreviation C has become more frequent, probably because it was widely seen as projecting a phrase CP since the late 1980s.

In languages exhibiting the Verb Second phenomenon the COMP position is the ultimate landing site of the finite verb in root clauses. Originally it was assumed that wh-phrases such as who in who did you see?, is in the COMP-position in order to explain why, in English, the presence of a wh-phrase usually excludes the presence of a complementizer (Doubly-Filled COMP filter). The standard assumption now is that COMP, or rather C'0, heads its own syntactic projection - CP - and that wh-phrases, relative pronouns and other preposed material are in the specifier position of CP.

Link
Utrecht Lexicon of Linguistics