It really doesn't  
I mean, USUALLY it includes the "GFE" of BBBJ and kissing. Many would say that it includes anal and CIM or COF. However, there are others who argue it's just a style- GFE is more sensual/romantic, PSE is dirty/raunchy porn-esque sex.  
Then,of course, there are actual porn stars who advertise a PSE, but don't do anal, CIM, etc- yet I think we can all agree it's certainly a porn star experience.  
Recently, "PSE" has been used to advertise uncovered full service/BBFS in a couple of west coast cities. Nowhere else in the adult industry uses that standard, yet it's now common there.  

The only (mostly) common denominator I've noticed, is that if there's an upcharge for PSE, then in those circumstances it usuallly includes anal. Still, in one of the cities where PSE is being used synonymously with bBFS, that might not apply and instead the upcharge is for uncovered services.  

 
See? It honestly is all over the map. If you expect a common definition of PSE and use that to find a provider then you're very likely to end up disappointed.  

Your best chance at figuring out what it means is simply reading a provider's TER profile and reviews, and perhaps backchanelling with previous reviewers.

"I think I'm entitled."

You want a common definition?!

"I want the truth."

You can't handle the truth!!  

The truth is, as was already stated, there is no "common" definition of PSE. Consider the one from Urban Dictionary.  While I'm sure some providers consider those services PSE, I know many "GFE" providers who don't consider those services PSE at all.  I also know many providers who use the term PSE synonymously with Greek, but that's not mentioned in the UD definition.  

If you're looking for exactitude, try mathematics.  You won't find it in p4p.

Actually there does not "have to be a common definition".  YMMV is a concept you need to come to terms with in this world.

You can also peruse the K-Girl forum for some discussion about the significant differences in the meaning of PSE that's been taking place on the west coast. You could also look at the situation of PSE and GFE -- some think GFE will be BBBJ while others argue it's more about emotional interaction and CBJ is well within the GFE scope and BBBJ would then be PSE. In other cases PSE indicate the provider will offer Greek (anal). In other cases the PSE is really about the lack of emotional, touchy-feely interaction and is just pure, raw sex and no cuddling.

Like with reviews, get to know how others use the terms so you can interpret what they are saying correctly.