Hello,  

Well, it generally refers to a process that allows you to accommodate a certain sized toy or fist. You begin with a smaller toy, and depending on the end goal, you either take multiple sessions to get there (like, if your goal is to take a fist), or you take an extended time within one session (like if you're goal is to be pegged with a small/normal sized toy).  This is from a dominant/top viewpoint. If the lady is submissive, she might be open to butt plugs, larger anal toys, etc.  

Thank you for the definition Miss Black,

I love anal play! Pegging, prostate massage, fisting, and all kinds of toy play. Check out my reviews; a lot of them mention anal play.

Not even kidding, that's what they're called!
And the last one...is not happening. Lol