opt-in
noun [ C or U ]
ukusthe fact that you do not have, receive, or join in something unless you choose to, or something that you do not have or receive unless you choose it:
Users have to click to give the company permission to collect data about their online habits, a process called opt-in.
We have a company pensions policy where there is an opt-in instead of an opt-out.
opt-in feature/system/policy The social networking site has introduced an opt-in feature for customers.
Compare
opt-out