Definition - What does Mil (mil) mean?
Mil is a unit of measurement in the foot-pound-second (FPS) British system, which is a thousandth of an inch (0.001 or 10-3 inch). It is also referred as a thou, a thousandth. In the USA the term mil is more widely used. A mil is equal to 0.0254 millimeter of the metric system.
Safeopedia explains Mil (mil)
A mil or thou are used to specify the dimensions in engineering or manufacturing. This includes measurements like the diameter of wire, thickness of a metal or plastic sheets, gaskets, gap of spark plugs, papers, films, printed circuit boards (PCB), foils, paint coatings, latex gloves, tolerance of hydraulic cylinders and fibers etc..
1inch= 1000 mils or thous
1 Mil = 0.001 Inch or 0.0254 millimeter
Compound units of mil (ex. mils per year) are used to express corrosion rates.