RPG is short for role playing game. Android RPGs will tend to be a large genre as it consists of many smaller sub-genres. Some of those sub-genres that will be found here are action role playing games (ARPG), strategy role playing games (SRPG), tactical role playing game (TRPG), massively multiplayer online role playing game (MMORPG) and Japanese role playing game (JRPG).
Most RPGs tend to consist of controlling a character or characters who are on some form of quest. This quest will take place in a detailed world and will contain many sub quests. There will also most likely be some form of a leveling system that often takes a good bit of grinding to get to adequate levels to advance on to the next section or quest. Of course many aspects will be dependent on the sub-genre of the title. Action role playing games often have a real time battle system, while Japanese role playing games tend to be turn based.