Free energy refers to the energy in a physical system that can be converted into work. It is a concept used in thermodynamics to describe the amount of energy available to do useful work at a constant temperature and pressure. The two main types of free energy are Gibbs free energy and Helmholtz free energy, which help predict the direction of chemical reactions and the stability of systems. In scientific contexts, free energy is important for understanding processes like chemical reactions, biological systems, and phase transitions. It helps scientists determine whether a reaction will occur spontaneously and how much energy is available for performing work in various systems.