Found it. I really should make a note of this, somewhere. These are MY definitions, obviously. Some people may quibble.
RPGs: main focus: player choice, characterisation and freedom of action. The player usually has a large amount of choice in what type of character to play, including race, sex, attitudes ('Alignment'), choices in dialogue trees, how the character develops skills and interacts with others, which companions to take along and which to leave behind, romantic choices, etc. The player is rarely straitjacketed in his movements, even from the start of the game, and will have a wide area to roam over. Decisions will often (Though not always) affect the plot (At least in some minor way) and there are often multiple methods to solve quests. EXP is given for quest completion and achieving goals as well as for killing enemies. The world is designed to be as real as possible to draw the player in and allow more choice of action. Combat is most often real time.
JRPGs: main focus: story and plot. The player usually has no choice of which character to play and very limited choice in dialogue or characterisation. No choice of companion or possible romances exists, no or very limited choices in interaction with others. The player will mostly be straitjacketed in their movements to start with, though the map will tend to open out with the acquisition of special vehicles. If you ever get to make decisions, they will be cosmetic only and have no bearing at all on the plot or story in any way. Solving quests invariably involves killing things. EXP is given for killing monsters only. The world exists wholly as a vehicle for the specific characters in the story and no attempt is made to make it look real, though mostly it does look incredibly beautiful. Combat is most often turn based.
Action-RPGs: main focus: combat: the player usually has a large amount of choice in how to configure their character for combat and how to upgrade their fighting skills. Any companions that may exist are combat support only and have nothing to say. Romance is certainly not on the agenda. The player can generally wander wherever they like in their quest to kill stuff. There are no real decisions to make and no plot to speak of as the entire emphasis of the game is on making the combat as fluid, interesting and exciting as possible. Solving quests involves killing things. EXP is given for killing things. The world is designed to be brutal, unforgiving and to generate vast hordes of opponents. It's possibly even less realistic than JRPGs in that every settlement should be overrun in seconds (As opposed to minutes for most JRPG settlements ;D). Combat is always real time, as the entire point of the game is to create a fast, furious and exciting combat simulation.
It's interesting to note that the worst RPG I've ever seen, Temple Of Elemental Evil is turn based (An utterly absurd choice as it's obviously designed to be hugely combat focused), whilst the best JRPG system I've seen is the one used by FF12, which is real time. In fact, the FF12 combat system is the best I've seen in any RPG of any type. The only real hard and fast rule for combat systems seems to be that Action-RPGs cannot be turn based. The rest is just habitual use by the programmers.
Please note the use of 'usually' throughout, as there are exceptions in all cases
