Grammatical aspect

Grammatical category expressing how a verb extends over time

In linguistics, aspect is a grammatical category that expresses how a verbal action, event, or state, extends over time. For instance, perfective aspect is used in referring to an event conceived as bounded and only once occurring, without reference to any flow of time during the event ("I helped him"). Imperfective aspect is used for situations conceived as existing continuously or habitually as time flows ("I was helping him"; "I used to help people").

From Wikipedia, under CC BY-SA. More on occurri.