Energy is the capacity to do work or cause change. It exists in various forms, including kinetic energy (motion), potential energy (stored energy), thermal energy (heat), chemical energy (stored in bonds of molecules), and electrical energy (flow of electric charge). Energy can be transformed from one form to another, but it cannot be created or destroyed, as per the law of conservation of energy. It is essential for all physical processes, powering everything from biological systems to machines and technologies.