What actually happens to those files that are "quarantined" or put into the "virus vault"?

Not much to add. Antivirus programs do it all the time and never explain. Are there leper colonies existing invisibly on my computer? Are the lepers from Spybot Search & Destroy in the same internment camp as Avast! rejects? Or are they just stripped of their last names and rendered helpless and left in place? Inquiring minds want to know