A deposition is where a witness or a party must answer questions under oath before trial. The deponent’s answers are transcribed. Today, many attorneys videotape depositions. Depositions typically take place in a conference room or office. The judge is not present.
During a deposition a lawyer will learn what a witness will later say at trial. A witness who contradicts his deposition testimony will come across as unbelievable at trial.
Depositions usually take place after the parties exchange documents. Lawyers can then ask deponents about the documents. For example, in a business litigation, an executive might be questioned for hours or even days about emails that he sent and received.
Below is a video on deposition I uploaded to my YouTube page: