Footprint
Footprint turns up in 2 fields: thermal spray, PCBs. Here is what it means to the people in each one.
Footprint in thermal spray
The shape of the deposit a gun leaves in a short stationary shot or single line, used to check spray alignment.
Spot or stripe sprayed onto a test plate with the gun held still for a moment or passed once, so the operator can see the shape and centering of the deposit. A round, centered footprint means good powder injection and alignment; a comet tail, offset or double peak points to wrong carrier gas, a damaged injector or a misaligned gun. Footprint width is also used to choose the index between passes.
"Shoot a footprint on the scrap plate, I think the injector got bumped when you changed hardware."
Footprint in PCBs
Pattern of copper pads, outline and markings on a board that matches one component package.
A footprint is the set of pads or holes, soldermask and paste openings, silkscreen outline and courtyard that defines where and how a component sits on the board. Footprints are built from the component datasheet or from IPC-7351 land pattern rules, which give density levels for least, nominal and most material. A wrong footprint, a mirrored pinout or a misplaced pin 1 is one of the most common reasons a first board fails.
"Footprint for the regulator has the pinout mirrored, we'll be dead-bugging that part on all ten boards."