Energy of activation refers to the amount of energy required to initiate a chemical reaction. It is an essential characteristic of chemical reactions since it determines whether a reaction is spontaneous or non-spontaneous. Energy of activation is also known as activation energy, which means the least energy required by particles in a reaction to reach the transition state and initiate the reaction. Other terms that can be used synonymously with energy of activation include the activation barrier, threshold energy, and reaction energy. These terms refer to the same concept of energy required to initiate a chemical reaction. Understanding the energy of activation is vital in the field of chemistry, where it helps to analyze and optimize the reaction kinetics of different chemical processes.