Gibbs free energy which is also called Gibbs function, Gibbs energy, or free enthalpy, is a term used to estimate the greatest amount of work done in a thermodynamic system while temperature and pressure remain constant.
The sign 'G' stands for Gibbs free energy.
At equilibrium:
The equilibrium given by is known as the spontaneous equilibrium.
This means that the reaction rate for both the forward and backward reactions will be constant.