Accuracy is one of the 4 weapon stats that can be upgraded. It is the probability the weapon hits the target. Decrease of accuracy is caused by weapon recoil or character's movements. It is increased by crouching.
You aim with the crosshair. Wider crosshair means worse accuracy. All weapons have better accuracy on closer ranges. Weapons that have short range also have worse accuracy, except Blades, which are melee weapons and therefore have almost perfect accuracy. Weapons with the best accuracy are obviously Sniper rifles, but it is also a common trait found among Rifles, Explosives and Elementals. Pistols are the secondary weapons with the greatest accuracy. Weapons with worst accuracy (with few exceptions) are Shotguns, Machine Guns and SMGs.
Accuracy gets worse by firing (recoil) and moving. While firing, the accuracy decreases by every shot. This has most effect with weapons with high fire rate, like machine guns, due to their extreme fire rate and bad accuracy. When you stop, it quickly turns back to normal. It also gets slightly worse while walking, and much worse while jumping. The Nervous flaw reduces accuracy in movement extremely.
Foregrip increases accuracy by 10% and without negative side effects.
Iron Grip offensive upgrade makes the weapon don't lose accuracy by firing and it has the same effect as Diazepam equipment. It works best with machine guns. With Steady Aim offensive upgrade equipment, weapon doesn't lose accuracy while character is moving/jumping, and it can be used against Nervous flaw. Crouch Master and Tripod give the character extreme accuracy while crouching.
Accuracy is the 2nd star in workshop upgrade machine. It increases the number of the accuracy bar for a little.