. Person who observes (witnesses) the signing (execution) of a legal document (instrument) and verifies its authenticity by putting his or her signatures on it. Certain legal instruments (such as deeds and wills) are valid only if properly witnessed by one or more competent witnesses.
2. Person who is called upon by the either side in a court case to testify or give evidence, and whose associated expenses are paid by the calling party. Such testimony or evidence may be given (1) orally in presence of a judge, (2) in the form of a sworn statement (affidavit), (3) via a live closed-circuit television, or (4) as a pre-recorded video.