Definition of opt-out:
(adj) :
Requiring a person or organization to choose explicitly to avoid or forbid something; tending to include by default; used particularly with regard to mailing lists and advertising.
(n) :
The act of opting out of something.
(n) :
(television, radio, countable) A regional broadcast that other stations in the network may elect not to include.
(n) :
(British, countable) A school or hospital that has withdrawn from local control.