A font is basically a set of numbered bitmaps.
Ok, many start out as vector drawings. But before they can be shown on the screen, they have to be turned into bitmaps. For each size. And there is a different one for bold and italic.
While those bitmaps themselves aren't protected, the names are. "Arial" is a copy-protected font name. You have to pay the owner if you want to use it.
You can copy it and name it something like "Liberation Sans". That would be totally legal.
And that's why you have "font families": specify a font name, and it will use the closest one available. But not all devices support that.
If you want the exact font, you have to render it into bitmaps first, and then upload it to the printer. User-defined fonts or graphics.
Anyway, it doesn't matter. If you use a POS printer, you are either printing receipts or labels, both of which have a very limited printing area. And the fonts supplied make the best use of that. Use them.