The limiting reagent is one that is consumed first in its entirety, determining the amount of product in the reaction. When the limiting reagent ends, the chemical reaction will stop.
In other words, the limiting reagent is that reagent that in a chemical reaction is consumed in the first measure, determining the quantity of products obtained. The reaction depends on the limiting reagent, because the other reagents will not react when one has been consumed.
I'm assuming that you are asking a general question because you did not include an example.
The limiting reagent is the item in the reactants (reagents) that will run out first. This is because it limits what the reaction can produce, essentially causing the leftover elements/compounds to just sit there.
This is takes into account how much of a substance should have been created (theoretical yield) and compares it to what was actually created (the actual yield).
