The verb disappear is normally an intransitive verb, but started being used as a transitive verb in this context (in English) to describe what happened during the US-supported fascist governments in Argentina and Chile in the 1970s and 1980s.
To the extent that information about imprisonment in Guantanamo Bay is kept secret from the families and lawyers of the prisoners, prisoners held there may be considered to have been disappeared from Afghanistan and Iraq by the US government.
Disappearances constitute a human rights violation.