Real Dictionary

opt out
phrasal verb: If you opt out of something, you choose to be no longer involved in it.

opt out in British English
to decide to leave or withdraw
adjective: permitting or relating to opting out
noun: the act of opting out, esp of local-authority administration
verb: to choose not to be involved (in) or part (of)

opt-out
An opt-out school or hospital has chosen to leave local government control and manage itself using national government money.