Admission against interest is an exception to the hearsay rule that lets a person testify to the statement of another person, which reveals something embarrassing, incriminating or something that might be considered damaging to the person making statement.
In terms of criminal law, admission against interest refers to the statement made by the defendant, which proves or supports a fact required to prove the defendant guilty. This can be evidence supporting the guilt of the defendant, but is not considered to be a confession.