A point is a physical measurement equal to 1/72 of an inch. Points are the most common way to size type outside of CSS (likely why it is supported in CSS).

What is CSS measurement units?

UnitDescriptionmmDefines a measurement in millimeters.pcDefines a measurement in picas. A pica is equivalent to 12 points; thus, there are 6 picas per inch.ptDefines a measurement in points. A point is defined as 1/72nd of an inch.pxDefines a measurement in screen pixels.

How big is a CSS pixel?

The term CSS pixel is synonymous with the CSS unit of absolute length px — which is normatively defined as being exactly 1/96th of 1 inch.