"Aftermarket" is a term used to describe parts that are not made by the factory. So for example, for your Eagle Summit, if you buy parts for your car that are not actually made by Eagle, then those are termed "aftermarket". Many people use the term "Summit aftermarket parts" specifically when referring to custom parts for the Summit, like performance parts or custom appearance parts. But even if you just replace your Summit brake pads with OEM-grade factory-style brake pads that are not made by Eagle, those too are aftermarket Summit 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".