A reversible reaction is a chemical reaction
where the reactants
that, in turn, react together to give the reactants back.
Reversible reactions will reach an equilibrium point where the concentrations of the reactants and products will no longer change.
A reversible reaction is denoted by a double arrow pointing both directions in a chemical equation. For example, a two reagent, two product equation would be written as
A + B ↔ C + D