Numeracy is the ability to understand and use numbers. May people understand the geometry because figures are easily understood. However many people do not understand the numbers associated with the figures.
Pythagorean thereom is an example. a^2 + b^2 = c^2. the numbers are harder to understand than the the triangle.
Perimeter and area are another example. People understand what length and width are, but once the numbers are supplied they do not see how to find the values.
I hope ths helps.