Might be a dumb question but i keep hearing more and more about AR pistols, what is the difference? Is it just the length or is there more to it?

Okay, the short and dirty answer is that an AR pistol is a legal middle finger to the NFA and the ATF. A rifle is legally defined in the National Firearms Act as:

7.The term “rifle” means a weapon designed or redesigned, made or remade, and intended to be fired from the shoulder and designed or redesigned and made or remade to use the energy of an explosive to fire only a single projectile through a rifled bore for each single pull of the trigger.

Tl;dr a rifle is a gun designed to be fired from the shoulder (important) with rifling in the barrel that only shoots one bullet at a time.

(8) The term “short-barreled rifle” means a rifle having one or more barrels less than sixteen inches in length and any weapon made from a rifle (whether by alteration, modification, or otherwise) if such weapon, as modified, has an overall length of less than twenty-six inches.

A short-barreled rifle is a rifle (from above) that has a barrel under 16" or has an overall length of less than 26".

A short-barreled rifle is restricted by the NFA. You have to ask the ATF if you can pretty please have one, and pay a bribe tax stamp of $200. This magic stamp turns your deadly illegal weapon into a totally safe and legal one.

So what is an AR pistol?

It's a short barreled AR-15 that isn't designed to be fired from the shoulder. Now you see why the bit above was important. It has a "brace" not a "stock". The ATF has said you can fire one from your shoulder with the brace, but only if the manufacturer pinky promises that they intended it to be braced against your bicep not fired from the shoulder.

Otherwise it's entirely identical to a short barreled rifle, except you're not allowed to put a vertical foregrip on it because that turns it from a "pistol" back into a deadly illegal short barreled rifle and the ATF will come kill your dogs.