A deposition is a discovery tool that is frequently used in lawsuits. At a deposition, a witness is asked questions and he/she must respond under oath.
A court reporter attends the deposition and transcribes the questions and the responses into a written transcript.
The witness is later provided with the transcript and allowed to make changes to it. The witness may have his/her lawyer present at the deposition.
Depositions in California are controlled by California Code of Civil Procedure §2025.