"Elfgames" seems to be occasionally used to refer to fantasy RPGs that are perceived as generic or escapist.
Where does the term come from and what was it originally used for?
What it's used for is easy. It's a tongue in cheek description of fantasy tabletop RPGs (mostly D&D) intended to say "We're just adults having fun - none of us should be taking this too seriously".
Google found me it being used in 2011 but nothing in 2010 which feels about right - and it seems to have spread from and around the Something Awful RPG forums (which are a lot nicer than the rest of the site). From there it mostly spread to RPG.net. Five years ago the Pathfinder/4e edition wars were still blazing and people needed to remind each other not to take it seriously.
Edit: for some links most of the SomethingAwful stuff is now archived alas - here's a rare example from the Paizo boards (from someone who at least was a regular at SomethingAwful). To get at it you need access to their archives or to find goldmined threads like this one from 2012. Here's a thread from RPG.net from 2013 discussing how it's used.