Dating questions whats your favorite Chate xnxx
It allows users' to add, edit, delete, upvote, down vote questions. You can charge the customer more if you claim it's a web application :) Seriously, the line is fine.
Historically, web apps were the ones with code and/or scripts (in Perl/CGI, PHP, ASP, etc.) on the server, and sites were the ones with static pages.
As I see it, a web site points to a specific page and a web application is more of some sort of 'portal' to content and information.
I'm not sure if there's an absolute authoritative answer to this, but you may look upon it as a distinction of what happens when the request hits the webserver.