The tense used to describe an action that had already been completed before another past action occurred.
Examples
Ich war zur Schule gegangen, bevor es regnete.
I had gone to school before it rained.
Er hatte Fußball gespielt, als ich ankam.
He had played football when I arrived.
Wir hatten Deutsch gelernt, bevor der Lehrer kam.
We had learned German before the teacher arrived.
See also
Verb
Tense
Present tense
Past tense
Present perfect tense
Future tense
Future perfect tense