Charge refers to how much Refrigerant / Freon is found in the Air Conditioning system. You can either have the proper charge, to much or to little of a charge. The last two are both bad & result in not only your unit not conditioning the air properly, but working harder than it is designed for.
It is imperative that your technician makes sure the coils, air filter, and blower are clean before “checking” the charge. If there is an issue caused by you not maintaining the unit properly, it can mimic a “low” level & adding more is not going to fix it for long. Along those lines, if you need some “added”, ask them where the leak is and has it been corrected… If their reply falls along the lines of “oh it’s normal for a system to need a charge every once in a while” you would be best showing them the door & finding a more experienced or trustworthy technician.