RPGS are all about statistics determining the results of actions, rather than the abillities of the player. The idea being that in a regular game you can't get past your basic limitations as a person, such as being weak, slow, dumb, or inherantly unlikable, in an RPG the idea is that someone can effectively take on the role of a character that is nothing like themselves and control it indirectly.
To understand what RPGs are you have to look at where they were invented, which also explains the meaning of the term. They did not just appear magically one day with an unknown origin, indeed we know pretty much where and when they were invented, and even who made them popular and put them into circulation.
RPGS are the child of wargames, which was where people would sit down and command armies to similate historical battles using sand tables and a lot of minatures, with statistics to represent each piece, and dice to determine the roll of fortune as to say whether an unreliable weapon like matchlocks were going to fire. As time went on they moved from historical simulation, into alternative history, and then eventually into pure fantasy as people found ways to try and simulate things like orcs and elves using the same numbers. Due to the price and complexity of entry you started also seeing these games reduce in scale from massive clashing armies, down to smaller, skirmish based confrontations where there was an increasing focus on invidual units and equipment. This eventually turned into the idea of games where each player would take on the role of a specific warrior and conduct the battle purely with statistics and dice.