What does a two-direction arrow indicate in a chemical equation?

In a chemical reaction, a two directional arrow indicates that the chemical reaction is reversible. A single directional arrow in a chemical reaction always indicates that it is an irreversible reaction. By a reversible chemical reaction, it means that the compound that is formed after reaction can be again broken down to form the compounds from which it was made. In case of irreversible chemical reaction it is not possible to return to the previous state from which the compound was made.