We don't use the name imperfect tense in English. The imperfect is a verb form, found in various languages, which combines past tense and imperfective aspect. It can therefore have meanings similar to the English "was walking" or "used to walk."In English we use past continuous to show an action that happened during the time another longer action was happening egI was walking to work and I tripped on the curb. -- The 'longer' action is was walking, the action that interrupted the longer action is tripped which is past simple