Deposition
Sworn, out-of-court oral testimony of a witness taken during discovery.
A deposition is the sworn oral testimony of a witness, taken before trial and recorded by a court reporter (and often by video). Counsel for all parties may attend and question the deponent. Deposition testimony can be used to discover facts, lock in a witness's account, and — under limited circumstances — as evidence at trial.
Depositions are a core discovery tool and are governed by FRCP 30 in federal practice.