Also known as the past continuous, the imperfect verb tense is used to describe events taking place in the past without regards to when the event began or ended.

The imperfect tense describes actions that:
• were happening,
• used to happen,
• or happened regularly in the past and on going.

The preterite is more akin to the English past tense, in that it specifies an exact time the action took place.

The examples below illustrate the difference with the word hablar (to speak, talk):

Imperfect
Ella hablaba.
She was talking.

Preterite
Ella habló.
She talked.