DJ Delorie replies: DJ found this description at diynetwork.com [Reprinted with permission from diynetwork.com]…
Jigs are devices that hold and move a work-piece in relation to a tool. Often they are designed as carriages that slide. Jigs act as a guide for the tools that cut and shape the wood, and they are ideal for repetitive tasks. By contrast, fixtures are static devices that hold the wood in stationary position in relation to a tool. Some of the more typical examples of fixtures are fences — such as a ripping fence on the table saw.
A good way to remember the difference is with the mnemonic: “A jig slides; a fixture guides.”
Dave Anderson replies: I suspect that most people use the terms jig and fixture interchangeably. In a more proper sense, a fixture is fixed or stationary like a light fixture and a jig is movable and/or removable. Another way of looking at it is that a workpiece is moved to a fixture while a jig is moved to the workpiece.
Jon Siegel replies: A fixture holds the workpiece but doesn’t have anything to do with locating the tool. For example if you want to drill a hole at an angle, you could build a wedge to hold the workpiece at that angle. But you still have to line up the drill in the usual (manual) way. So the wedge is a fixture