In the case of AutoDock Vina, the docking score is the binding affinity which is the change of free energy.

Nayim Sepay it means that low binding affinity means strong binding? right? for example if compound A binding affinity score -11 and compound B binding affinity score is -9, does it means that compound B forms weak receptor-ligand binding or opposite?

Well Thank you Nayim Sepay for response

In your case, the compound A is strong binder than that of B.

Thanks a lot guys Nayim Sepay & Akansha Agarwal it helped me a lot

While you are performing docking using Autodock Vina, you get a ranked binding energy in the log file (lowest binding energy at the top). Lowest binding energy (usually negative) means more stable complex formation between receptor and ligand.