Is this a loft or a mezzanine? What's the difference between a loft and a mezzanine?

I have circled it in blue.

I would call that a loft. In fact, I have only heard "mezzanine" used to refer to some kind of seating in a theater. That sort of thing.

That's a additional floor created from a space with a high ceiling using a steel construction. The additional level is called a mezzanine floor. A loft is a space right below a roof whereas a mezzanine floor could be on any floor