During a deposition, a party or witness' out-of-court testimony is
taken. For example, an expert witness is deposed to determine what his
opinions are. The deponent is asked questions by attorneys representing
the parties in the case. Testimony is given under oath. Deposition testimony
is usually recorded by a court reporter.
The transcript of the deposition can then be used throughout the case.
For example, during trial, an attorney who is questioning a witness may
use that witness's deposition testimony to point out inconsistencies
in the witness' trial testimony.