ADP (Adenosine Diphosphate): This is what remains after an ATP molecule has been used for energy. It's like a depleted battery that can be recharged back into ATP.
The process by which ADP gets recharged into ATP. It's similar to plugging your drained phone into a charger.
Energy Coupling: The use of energy released from an exergonic reaction to drive an endergonic reaction, often involving the transfer of phosphate groups from ATP molecules. It's like using the heat generated by your laptop (an unwanted side effect) to warm up your hands on a cold day.