What is delegation, identity delegation, and delegated authorization, and what are the differences among them?

I’ve been writing up a guide to OAuth 2.0, OpenID Connect, and Identity Server 4 mostly for my own learning, drawing on several sources such as OAuth2 In Action, OAuth 2.0 Simplified, and CISSP: A Comprehensive Beginners Guide on the Information Systems Security, but I’m having trouble finding explicit definitions of delegation, identity delegation, and delegated authorization along with how they’re different (if they are).

This wikipedia article comes the closest to what I’m looking for, but its sources seem a bit questionable to me:


OAuth2 In Action and OAuth 2.0 Simplified both have explicit definitions for delegation and describe them as “letting someone who controls a resource access that resource on their behalf” and “allowing third-party applications to act on behalf of a user, without the application needing to know the identity of the user,” respectively, but based on my reading these both actually describe delegated authorization or delegation of authority.

Would anyone care to take a crack at defining these or point me to something I could read to help me clear these concepts up in my head?