I think this tag could apply to several of the posts on this site, and is a good canonical name describing the intention of a challenge.
It could possibly be a tag accommodating different types of challenges, but I see it as mostly accommodating a code-golf challenge. A challenge would be given this tag if it asks to create a function or language construct to accomplish a task, and restricts answers from using the language's exact and similar built-ins within the implementation.
I find that fleshing out exactly what "similar" means in this case would be in the interest of the community to balance creativity and close loopholes in the spirit of preventing the challenge from becoming too trivial. My question, however, is not proposing to define what that means yet though, just whether this tag should exist or not.