Something that is perfect is complete and without defect or blemish. It might also be precisely accurate or exact.
The word perfect can also be used as a verb meaning — you guessed it! — to make something perfect. (Note, though, the pronunciation difference: PER-fect as a noun; per-FECT as a verb.) It originally comes from the Latin word perficere, which breaks down into per- ("completely") and facere ("do"). As a noun perfect is a grammatical term referring to a tense of verbs describing an action that has been completed.