OPT-OUT is an unsubscribe request
An OPT-OUT request means you are unsubscribing for something. This usually occurs in email newsletters that you receive. Often, at the bottom of such a newsletter, there is a possibility to unsubscribe, sign out, or unregister. For domain names you can also opt-outen. Then it means that the address data does not emerge if one does a whois on the domain.