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