Past continuous is a verb tense also called past progressive. It is used for continuous actions in the past.
Subject + Was/Were + Verb + ING
I was sleeping.
They were dancing.
Past continuous is used to show an action that was continuing in the past until another action interrupted it.
The continuing action is past continuous and the interrupting action is simple past.
I was sleeping when you called me.
(The action of sleeping was continuing over time until the telephone call interrupted the sleeping.)