What does it mean when a math problem is undefined?

Answer 1

When a math problem's answer is "undefined", that means that it's an impossible answer, such as 3/0. A number can't be divided by zero because 3/0, as a word problem, would be, "How many times does zero go into three?" Since there is no real answer, they just call it undefined. Note that it can only happen with division problems, and not multiplication, addition or subtraction problems, since 3*0 is 0, 3+0 is 3 and 3-0 is 3. An undefined answer can also be in linear equations, if the line is flat (horizontal), then the slope is 0, or undefined.

Simplified answer: if any number is divided by zero, it is undefined, even 0/0. In equations with slopes and lines (linear equations), if a line is horizontal, it's slope is undefined.