What is a charge cycle ?

well i am getting my u36sd laptop today, and like most people i would want to know how to save my charge cycle, well then this question come up.. what exactly is a charge cycle, how is it define ?

i mean i know, at least i think when i say use 50% of the battery, then i go recharge it, i just waste a charge cycle. so does that mean using it down to 30% battery and recharge it also cost 1 charge cycle ?
then what about i only use .00000001% of the battery, then go recharge it, does it cost me a charge cycle, it is an important question to me because say if ur laptop is always plugged in when u turn it on, it should not waste any charge cycle, but battery does lose a very tiny bit of charge on it own, so if every time my laptop is off, i bring it to a classroom, and plug it in there, my battery should discharge a very tiny bit of charge, and if it count as a charge cycle then i will be burning those charge cycle, instead of saving them.

help please.. i am probably posting in the wrong place.. but hey it is the battery of my asus notebook
and a side question, do you check the content of the box before u sign when u receive shipment from ups ?