A failure in a maths exam or test. Or a failure involving any maths-related problem or scenario. Dervies from the word Maths, (M) Addition, (a) Numbers, (N), Division (D) and Obtuse, (O). Commonly used in the east-Midlands area of Britain, this word is growing in usage.
Teacher: What do you think of the fact that you got 25% on your Maths exam?
Boy: It's a Mando-fail.