was doing something (past continuous)
Describes an action or state that was ongoing at a point in the past.
This pattern is the past tense of ている. It expresses that an action was in progress or a state continued over a period in the past. It's the standard way to say 'was doing' in Japanese. For example, if you were in the middle of watching a movie when the phone rang, you'd say 映画を見ていた (I was watching a movie). It's also used to describe a past state that lasted, like living somewhere or having a habit. Note that for verbs like いる (to exist) or ある (to exist inanimate), ていた can also indicate a past state of existence, though いた alone is common for people or animals.