[eh-fen-dim] int.
What was that? / Yes? / What do you need? / What is it?
DT: My master / my lord
Notice the slight pronunciation difference!
When you don’t understand what someone said but not because of a language barrier – because they mumbled or from some other external barrier. It’s also used when someone understands everything very clearly but they’re in such shock that they want to make sure they heard you right.