Imperfective

The imperfective (abbreviated IPFV or more ambiguously IMPV) is a grammatical aspect used to describe a situation viewed with interior composition. The imperfective is used in language to describe ongoing, habitual, repeated, or similar semantic roles, whether that situation occurs in the past, present, or future. Although many languages have a general imperfective, others have distinct aspects for one or more of its various roles, such as progressive, habitual, and iterative aspects. The imperfective contrasts with the perfective aspect, which is used to describe actions viewed as a complete whole.

English is an example of a language with no general imperfective. The English progressive is used to describe ongoing events such as "The rain was beating down". Habitual situations do not have their own verb form (in most dialects), but the construction "used to" conveys past habitual action, as in I used to ski. Unlike in languages with a general imperfective, in English the simple past tense can be used for situations presented as ongoing, such as The rain beat down continuously through the night.

A contrast between the progressive and imperfective is seen with stative verbs. In English stative verbs, such as know, do not use the progressive (*I was knowing is ungrammatical), while in languages with an imperfective, stative verbs frequently appear in the imperfective.

Verbs in Slavic languages have perfective and/or an imperfective form. Generally, any of various prefixes can turn imperfectives into perfectives;suffixes can turn perfectives into imperfectives. The non-past imperfective form is used for the present, while its perfective counterpart is used for the future. There is also a periphrastic imperfective future construction.

...
Wikipedia