Say you’re designing the character creation rules of a fantasy RPG (pen-and-paper or video game). Nothing fancy, just a few ability scores picked using a point-buy system and improved as the character gains levels. So far so good. But you also want to show off the amazing diversity of your fantasy setting, so you write something like this:
Elves are swift and gracious compared to clumsy humans. Elf characters get +2 Dexterity.
Seems reasonable on its face, and damn near universal in gaming. But what does it actually mean?