Identification, Authentication, Authorization
These three terms are related, but mean different things. Here’s my shortest explanation ever:
Identification: who wants to act on the system? User John, with ID johndoe? Ok!
Authentication: is it really John though? Let’s check if his username & password match. They do, so it is John indeed! Cool stuff!
Authorization: John wants to delete post with ID #5. Is he allowed to do that? Well, post #5 doesn’t belong to John, but John is an admin, so can delete the post. Sweet!