"Aftermarket" is a term used to describe accessories that are not made by the factory. So for example, for your Suzuki Esteem, if you buy accessories for your car that are not actually made by Suzuki, then those are termed "aftermarket". Many people use the term "Esteem aftermarket accessories" specifically when referring to custom accessories for the Esteem, like performance accessories or custom appearance accessories. But even if you just replace your Esteem brake pads with OEM-grade factory-style brake pads that are not made by Suzuki, those too are aftermarket Esteem accessories. Over the course of a vehicle's life, it almost certainly will have aftermarket accessories installed in it at some point, even if the vehicle is never actually "modded out".