The nm numbers are just an attempt to extrapolate using the transistor density increase. 5 nm means something like "it has the same transistor density as if we

The nm numbers are just an attempt to extrapolate using the transistor density increase. 5 nm means something like "it has the same transistor density as if we shrunk transistors from about 20 years ago to 5 nanometers". It's more familiar to people than transitioning to "transistors per square micrometer".