What do you mean by limiting reagent?

Some -times in a reaction, the amount of one reactant may be more while that of another may be less than the required from the balanced chemical equation. The amount of the reactant which is less will get used up earlier and hence limits the reaction. Such a reagent which is used up first in a reaction is. called limiting reagent. For example, here in the following reaction

suppose 2 moles of H₂ are reacted with 2 moles of O₂ to form water. According to the above balanced chemical equation. 2 moles of H₂ require 1 mole of O₂ for complete reaction. Therefore, there should be 4 moles of H₂ to react with 2 moles of O₂ but H₂present is only 2 moles. Hence, H₂ is a limiting reagent which will get used up earlier when only 1 mole of O₂ would react leaving behind 1 mole of unreacted oxygen.