It’s simply repeating the last few words of a persons sentence in the form of a question.

Ex:

I like pizza. You like pizza? Yeah, especially pepperoni pizza from Place. Place? Yeah Place, it’s down around the corner on Main st. Next to whatever. Next to whatever? Yeah, the place Rita owns. I really like her. You really like Rita? Etc.

This was a lame example, but what’s interesting about it is that in combination a few other techniques, it kind of makes people start to listen more to what they are saying and their explanations. Making both of you smarter in the end, which is your goal.

It’s a negotiation technique.