It is a molecule in the cell called adenosinetriphospate where the name comes (A from Adenosine T from tri and P from phosphate). It is a molecule with three phosphate groups and there is a high energy bond between the outer two ones. This molecule is able to store a certain amount of energy and give it to any molecule in the cell that needs this energy to function. Glucose has a big amount of energy that cannot be used all at once and directly by the different types of molecules in the cell so this energy is released during respiration and stored in smaller chunks in several ATP molecules which could be used one at a time to release this specific needed amount of energy. This is a kind of control for the excess energy coming in glucose does not harm the cell when not needed
