Some people call it Multiplayer Online Battle Arena (MOBA), Valve is calling the upcoming Dota 2 a Action RTS (Real Time Strategy) and I've seen some using Action RPG.
Has the community come to an understanding?
I do not play these games much (or well :P) so I don't know.
Best Answer
According to Riot's official description of League of Legends, available here:
Bolded emphasis mine.