Perfect Aspect (definition)
A sentence marked for perfect aspect conveys the meaning of a state in the time conveyed by the tense that is due exclusively to a past action. The aspect occurs in all three tenses. In Scottish Gaelic, perfect aspect is marked by the particle 'air', which is homophonous and homographic with the preposition meaning 'on'.
Crystal, David. A Dictionary of Linguistics and Phonetics. The language library. Oxford, UK: Blackwell, 1997.