Definition: The tense that expresses action in the past that has not been completed, that occurred habitually or frequently or that took place over an indefinite period of time. It is contrasted with the preterite tense, which expresses action that took place at a definite time or has been completed. English does not have an imperfect tense per se, although it has other ways of expressing the concept of the Spanish imperfect, as in the examples below.

Also known as: Pretérito imperfecto in Spanish.

Examples:

• Él cantaba. (He used to sing.) The English translation shows how the activity occurred at an indefinite, extended period of time.
• Ella escribía la carta. (She was writing the letter.) Note that in this and the above example, out of context the verb doesn't indicate when or even whether the action came to an end.
• Yo conocía a Eva. (I knew Eva.) Conocer can mean "to know" or "to meet." The use of the imperfect here shows that the activity took place over an indefinite period of time, so "knew" makes sense here.