Jacket Copy and Blurbs

I’ve been researching and learning about jacket copy and blurbs. What I’ve learned is that a blurb is written by a different author about your book. Is jacket copy always written by the author or do some publications write that for the book? To make things more confusing, I often see jacket copy referred to as a blurb (I think) and it’s messing with my OCD brain.

What is the professional opinion of any professional editors, publishers, agents, authors on the site?