RPG is mostly games where you build your character up with a system of stats.
and battles take place similar to a D&D setting

Character development, story, and towns are emphasized....

theres dungeon-->town--->exploration afoot....

Its often menu driven. Only in rare cases (action RPGs) is it not totally "menu driven"

Basically its games similar to an electronic implementation of D&D or other pen/paper RPGs.

Yes you're playing a role in say, Halo, but it doesn't contain the same immersive story/world elements that make it a deeper game than a normal FPS...

Some games COULD be said to be RPGs, but often have a more predominant genre... like Zelda, it is more action/adventure than action RPG.

somethin' like that.