1. imperfective - Noun
2. imperfective - Adjective
aspect without regard to the beginning or completion of the action of the verb
Source: WordNetAlthough languages that are described as having imperfective and perfective aspects agree in most cases in their use of these aspects, they may not agree in every situation. Source: Internet
Explicit consideration of aspect as a category first arose out of study of the Slavic languages ; here verbs often occur in the language in pairs, with two related verbs being used respectively for imperfective and perfective meanings. Source: Internet
In addition to that, past compound forms using participles vary in gender (masculine, feminine, neuter) and voice (active and passive) as well as aspect (perfective/aorist and imperfective). Source: Internet
Although the verbs' meaning is similar, in perfective verbs the action is completed and in imperfective verbs it is ongoing. Source: Internet
Common 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