"After-market" defines a Jig, Fixture, or other type of accessory designed to upgrade the utility of a tool, usually a power tool, which, developed by a craftsman in a shop, has been patented and placed on the market.
A ready example is the 1950s Biesemeyer Fence for Tablesaws.
Another is the Paralok Fence System, introduced in the 1980s but -- now -- evidently longer sold.
After-market, as a term, evidently originated in the auto industry in the 1930s. After market accessories are, at bottom, Jigs and/or Fixtures, and more than anything else, demonstrate conclusively that woodworking is a "bottom-up" activity. [more on this later.]
Below is a temporary fix -- actually a favor for a friend -- but useful all the same, if you are new to the concept of after-market jigs and fixtures. The prevailing meanings of jigs and fixtures makes the device in the images below a "fixture"-- fixture because it is attached to a power tool -- read more here.
This fixture -- a means of creating a "table" for a router by utilizing space on a tablesaw's table-top -- replaces one side of a table-saw's cast iron table-top. I used this device for several years, after purchasing my first router in the 1980s. Later, though, I made my own router table, because there were too many downsides having this fixture -- with router mounted -- with simply operating my table saw. For example: with the router mounted, I couldn't tilt the saw's arbor.