Perfects in English grammar are words that express the perfect aspect.
Perfect is a grammatical function.
The grammatical form that can function as the perfect in English grammar is the verb phrase. The only auxiliary verb that can function as the perfect is the verb have.
Perfects are constituents of the verb phrase.
Brinton, Laurel J. & Donna M. Brinton. 2010. The linguistic structure of Modern English, 2nd edn. Amsterdam: John Benjamins Publishing Company.
Hopper, Paul J. 1999. A short course in grammar. New York: W. W. Norton & Company.
Huddleston, Rodney. 1984. Introduction to the grammar of English. Cambridge: Cambridge University Press.