Why ATPs are Called Energy Currency of The Cell
In day-to-day life, we use money as a common medium to exchange value ("value" here means products or services). For example, we give value that we have to others and get money in return. Then we use that money to get values that we need from others. Thus we use money to exchange values.
Similarly, in the cell, ATPs are used as a common medium to exchange energy. Energy from different high-energy molecules is packed in ATPs. Thus a single pool of ATPs is generated as a source of energy. Then when energy is required for any reaction, it's obtained from ATP. Thus ATPs serve as a common medium to exchange energy. So ATPs are called the energy currency of the cell.