Your question consists of TWO difficulties:
the name of the unit and the actual size of a character.

[1] The point"

The "point" (as a measuring unit for type) dates back from a very long time, when monks and publishers wanted to associate their system of measurement with other units of measure, like geography and carpentry. So they teamed up and took their smallest element (the tiny dot of their pen) and found a way to let it correlate with other units.

Using divisions of 6 and 12 (just like with time and sizes), they came up with the pica (12 points), and 6 picas add up to 1 inch. Ao if you type in "1p" as the font size in Adobe InDesign, it will return "12 pt". Easy !

So all in all, there are in total 6 picas x 12 points = 72 points in 1 inch, which was not just good enough for typography in the Middle Ages, but also good enough for the first black &; white screens of the first Apple Macintosh computer ! That's why computer screens originated at "72 dpi". (Modern screens are much finer nowadays, so 1 point doesn't equal 1 pixel anymore.)

Back to typography: all over Europe there were many publishers and type sizes, with slightly differed in absolute sizes, due to the size of the foot of the ruling King in an era. Type in "1c" in InDesign (1 cicero being the equivalent of 12 didot points), and it will return "12,788 pt", which indicates that the French King had larger feet than the concurrent English one...

The English inch size also changed over time, even twice after it had already spread across North America. So American software like Adobe InDesign actually defaults to a outdated English type size ! Fortunately, computers can calculate and convert all figures to anything, so it really doesn't matter so much anymore which unit you prefer. But any old fashioned type size is still easier to work with than that synthetically devised decimal meter.

[2] The font size

That mystery is also surprising but a bit easier to understand. The font size does not describe the size of a character itself, but the piece of wood it was cut from, or the piece of metal it was cast in. So it's the little body of wood or lead that has the given size in its height. That also explains why we sometimes say "corps 12".

The type designer can fairly freely use that height to create the characters in. That's why an Arial 12 appears so much larger than a Times 12 font ! They share the same space, but in varying sizes.

Above: Times, Arial, and Futura, all at corps 36 pt !

All mysteries cleared up now ?

Oorspronkelijk geplaatst op Quora: "Text either Arial or Times New Roman 12 point." What does "12 point" mean? Does it mean the font size is 12?"