the 2nd hand market for parts to keep up gear. Most are large. AKA replacement marketplace or additional market.
1940, American English, of vehicle components, from after + marketplace.
additional market that supplies accessories, free components, second-hand gear, alongside goods and services used in restoration and upkeep. Some aftermarkets, like those for automobile accessories, parts, tires, tires, have become large. Also referred to as replacement marketplace or secondary marketplace.