Energy is defined as :

• Energy is the capacity to do work. 
• An object that possesses energy can exert a force on another object. 
• When this happens, work is done on the object due to which energy is transferred from the former to the latter. 
• For example, when we lift an object, we apply some energy due to which work is done on the object. This work done on the object gets stored in the form of a potential energy of the object.

Therefore, we can say that energy is the capacity to do work.