Hi irsyadist,
An Apple Store, or an Apple online store is a store run by Apple themselves. If you buy from there you'd be buying directly from Apple, which will get you your product for a fair price.
An Apple reseller is a separate company that is partnered with Apple, and has a deal with them to sell Apple products at their store. Apple resellers exist mainly in countries or areas where there are no official Apple stores. You will often pay higher prices to buy off an Apple reseller, however they may also do special deals with you if you buy more than one product from them 😉
Hope that cleared it up?