Anything numerical is related to numbers or can be expressed in numbers. Your height is a numerical concept, but your love for your friends is not.
You will learn many numerical concepts in math class: anything that has to do with numbers in any way can be referred to as numerical. Mathematicians deal with numerical issues, but poets do not — unless they're counting syllables, which is numerical because it involves numbers. Some people are better with numerical concepts than others — like accountants, statisticians, and math teachers.