Noun
the aspect of a verb that expresses a completed action
Source: WordNetCommon aspectual distinctions The most fundamental aspectual distinction, represented in many languages, is between perfective aspect and imperfective aspect. Source: Internet
Consequently each language contains many pairs of verbs, corresponding to each other in meaning, except that one expresses perfective aspect and the other imperfective. Source: Internet
The imperfective aspect typically indicates that the action is unfinished, in progress, or repetitive; while the perfective aspect typically denotes that the action was completed, instantaneous, or of limited duration. Source: Internet
The perfective aspect verbs also use the perfect passive participle in the passive voice. Source: Internet
This is the perfect stem, and it is used for all of the tenses in the perfective aspect. Source: Internet