What does pbw stand for?

Answer 1

I want to answer this in as cool, oblivious, G-rated, not to mention snide a manner as possible. So I'm gonna give you what you don't want, ie:

Play By Web

Peanut Butter Wolf

not to mention

Proton beam writing

and especially

Prosopography of the Byzantine World

instead of what you do want, for which I will refer you, as ever, to Urban Dictionary.

In short, though, and because I can, I will tell you it means one uses, say, digitus secundus manus, somewhere one's great grandmother never mentioned to do something one's great grandmother refused to acknowledge ever happened. If, indeed, that is not enough information for you, well, you do know where to go, do you not?