Battery cycles are usually referred to as a common measurement unit for batteries. A single battery cycle is defined as a one 100% use and subsequent recharge of the battery.
For example, if a user had 100% battery on their laptop in the morning at work, and in the afternoon had 0%, but then at night, went home and charged it up to a full 100%, that user’s laptop had just completed 1 battery cycle.
Battery cycles are usually used as a measure of a battery’s age and wear. Batteries don’t hold capacity as they age. As batteries go through more cycles, their capacity decreases. Batteries are usually rated for a certain amount of cycles.
Most manufacture rate their batteries to hold up to 80% of their original designed capacity. This means that if a laptop was rated to hold 80% their original capacity of 4000mAh for 1000 cycles, then after 1000 cycles, the battery should still have 3200mAh of capacity.