The document explains the past continuous tense in English grammar. It provides examples of using the past continuous to describe actions that were happening at a specific time in the past, such as "I was playing football at 3 pm yesterday." It also discusses using the past continuous along with the past simple tense to talk about two simultaneous past actions, like "Sam hurt himself when he was jumping over the vaulting horse." The document then provides an example story and exercises to practice using the past continuous tense.