(1) The equilibrium constant for a reversible chemical reaction.
(2) The ratio depicting the concentrations when chemical equilibrium is reached, and expresses the extent to which equilibrium has favoured in either direction.
The equilibrium constant is represented by Keq in an equation. If Keq is greater than 1, it means the concentrations of the products are greater than those of the reactants, and forward reaction is favoured. If Keq is less than 1, it means the concentrations of the reactants are greater than the products, and the reverse reaction is favoured. If Keq is 1, it means neither forward nor the reverse reaction is favoured.
See also: chemical equilibrium, free energy.