- Of a selection, the property of having to choose explicitly to join or permit something; a decision having the default option being exclusion or avoidance; used particularly with regard to mailing lists and advertisement.
- They set up an opt-in mailing list, so that those who wanted the notices could subscribe.
opt + in
(third-person singular simple present opts in, present participle opting in, simple past and past participle opted in)
From opt + in.