Final answer:
A coefficient is a number written in front of a chemical formula to represent the number of moles of a reactant or product in a chemical equation.
Step-by-step explanation:
In a balanced chemical equation, the number that is written in front of the element or compound is called a coefficient.
A coefficient represents the number of moles of the reactant or product involved in a chemical reaction.
For example, in the chemical equation: 2H₂ + O₂ → 2H₂O, the coefficient '2' in front of the H₂O indicates that two moles of water are produced when two moles of hydrogen react with one mole of oxygen.