FontSize is an option for Cell, StyleBox and StyleForm which specifies the default size in printer's points of the font in which to render text.
The size of a font is typically taken to be the distance from the top of the highest character to the bottom of the lowest character.
A printer's point is approximately of an inch.
Fonts with the same nominal point size may not look the same size to the eye.
See Section 2.9.9 and Section 2.11.10.
See also: FontWeight, FontTracking, ScriptMinSize, ScriptSizeMultipliers.
New in Version 3.