Which term refers to the formal process of questioning a witness under oath?

The term that refers to the formal process of questioning a witness under oath is "deposition." A deposition is typically conducted as part of the discovery process in legal proceedings, where an attorney questions a witness, and the responses are recorded for later use in court. This process ensures that both parties can gather relevant evidence and testimony before trial.

During a deposition, the witness is legally obligated to answer questions truthfully while under oath, which helps to establish a reliable account of facts and circumstances related to the case. This recorded testimony can be pivotal in the trial, either supporting or challenging the evidence presented.

The other terms do not specifically define this formal process. "Interrogation" usually relates to law enforcement questioning and may not always occur under oath. "Testimony" pertains to the actual evidence presented by a witness during a trial or deposition. An "affidavit" is a written statement that is sworn to be true, but it is typically not a verbal questioning process. Hence, "deposition" is the most accurate term in this context.