The reactant that will be exhausted first.

In chemistry, the limiting reagent, or also called the "limiting reactant", is the chemical that determines how far the reaction will go before the chemical in question gets used up, causing the reaction to stop. It is determined by working out the balanced equation for the chemical reaction, comparing how many units (mols) of each go into the reaction (in a proportion), and then measuring how many mols of each chemical will be used in that reaction. The chemical of which there are fewer mols than the proportion requires is the limiting reagent.

Can be the opposite to reagents by limiting the effect of a chemical reaction.