Final answer:
The reactant that is completely consumed in a reaction, restricting the amount of product formed, is known as the limiting reactant.
Step-by-step explanation:
The name for the reactant that is entirely consumed by the reaction is the limiting reactant. In chemical reactions, when reactants are not present in stoichiometric quantities according to the balanced chemical equation, one reactant will be used up completely while others may remain in excess.
The limiting reactant determines the maximum amount of product that can be formed, as the reaction proceeds only until this reactant is completely used up. Identifying the limiting reactant is a crucial skill in chemistry, as it allows for the calculation of theoretical yield and helps in understanding reaction dynamics.