The state in which the rates of the forward and reverse reactions are equal, and the concentrations of the reactants and products remain constant.
Direction of the reaction
The direction in which the reaction occurs, i.e., whether it's the forward or reverse reaction.
Forward reaction
The reaction in which reactants are converted into products.
Reverse reaction
The reaction in which products are converted back into reactants.
Le Chatelier's principle
A principle that states that when a system at equilibrium is subjected to a stress (such as a change in concentration or temperature), the system will respond by shifting the equilibrium in the direction that reduces the stress.
