What do you mean by delegate? Can a user retain delegates?

A delegate is an object, which acts on behalf of, or in coordination or sync with, another object when the other/second object encounters an event during program execution.
Delegates can be retained if the user wants to. If the user declares it to be retained (which means the delegate will be influential in ARC) it’ll be retained.
Generally, the norm is not to retain the delegates because they are already retained elsewhere and more importantly, the user can avoid retaining cycles by opting not to retain them.