APU stands for Accelerated Processing Unit, it is a CPU which has it’s own GPU (Graphics Processing Unit) onboard so it doesen’t require a dedicated graphics card.
The Potato APU Score is, unlike other benchmarks, purely based on the gaming capabilities of the tested APU and roughly resembles the achivable average framerates in 1080p on LOW quality settings. For Example, a Potato Score of 25 equates to 25 FPS.