What does popularity ranking actually mean

Stephanie

and how popular is Luna? I know the top #100 means a name is popular but how popular? If a name is ranked #50 will there be three other girls in her class with the name or is that only if it’s in the top ten? Or what about #20?

Wondering because my hubby loves the name Luna, but I’m worried it’s too popular. I don’t need a unique name no one else would have... but would like to avoid multiples in the same grade.