The process in discovery of taking sworn testimony from a potential witness in a court case, usually recorded in at least a transcript and also frequently on video. A deposition is considered an extension of the court case and as such, evidence taken at a deposition is usually introducible in court. In the United States, depositions can sometimes be difficult affairs, which has led some wits to describe them as displays of “lawyers behaving badly.” See Objection!
Typically a deposition, especially in US proceedings, will be taken by a state-licensed court reporter.