A captive in bondage or BDSM play is the person who is tied up or imprisoned. Such a person will often, but not always, be a sub, bottom or masochist. The term prisoner may be preferred if the emphasis is on the imprisonment rather than bondage.
In general, a captive can always be regarded as a victim. The converse is not true, since a victim may be someone who is punished but not held captive. If the emphasis is on punishment rather than captivity, the term "victim" should be used.
The term does not imply that the person is unwilling; informed consent must always have been given in advance.
In the Gor series of science-fiction novels by John Norman, a "captive" or "prisoner" is someone who is lawfully under the full control of another person (thus not illegitimately kidnapped), yet not legally a slave (see Gor - Dictionary).