The point is a unit of length in the field of typography and uses the symbol pt.
It is the smallest unit in the world of typography. There are 12 points in a pica.
In physical printing methods / press systems, the point size is the height of the metal press body on which the font's letters are made. When applied to the digital type space, letters are designed around a theoretical size, an em square which is scaled to the relative point size (when specified of course!).
The mil is a unit of length in the imperial unit system and uses the symbol mil (or sometimes thou).
A mil in one one-thousandth of an inch (0.001 inches) or 25.4 μm.
The mil is still used in the US to measure thickness of various materials.