The excess reagent is that reagent in a chemical reaction which has a greater amount than the necessary amount to react completely with the limiting reactant. It is the reagent that remain after a chemical reaction has reached equilibrium.
Limiting reagent is that reagent in a reaction that will limit how much product can be formed. It is the reagent that can not remain after a chemical reaction has reached equilibrium.
N2+3H2→2NH3
For example if we have 6 moles of N2 and 5 moles of H2. This means that you will only be able to make 3.5 moles of NH3 rather than 4 moles because we don’t have enough H2. In this case, N2 is the excess reagent and H2 is the limiting reagent.