Innumerate means “unfamiliar with mathematical concepts and methods” – in other words, innumeracy is another way of saying “numerical illiteracy”.
I never knew there was a word for it, but I’m definitely familiar with the concept. Even though I’m technically a math major, I’m still innumerate when it comes to leaving a tip! Funny how you can be good at calculus without being able to do simple arithmetic.
The opposite of innumeracy is numeracy (short for “numerical literacy”). According to Wikipedia, those two terms were coined by two different people, thirty years apart.