Basically 1 cycle can be made up of any number of charges which add up to 100%.
Thus charging from 80% to 100% = 20%, from 90% to 100% = 10% and so on, adding each charge percentage up until you score 100. Each cycle wears a battery down by a small amount so a partial discharge before charge is better than a full discharge.
Also note that battery charge levels and health are not an exact science. The cycle count is based on "educated guesses" made by your computer's Systems Management Controller (or SMC, for short). It is helpful to periodically "calibrate" your battery by using the machine until it goes to sleep on its own (i.e. completely out of battery power) and doing a full recharge before you use the machine again.
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