What does "inverse" mean in math?

In math, inverse is explained as the opposite in effect. An inverse function is one that reverses another function. If an inverse does exist for a function, it is referred to as an invertible function.

The inverse of the operation of addition is subtraction. An example of this would be the following reversal: the inverse of 20 + 9 = 29 is 29 - 9 = 20.

The operation of multiplication has an inverse operation of division. Multiplication can essentially be reversed by division. An example of this is 5 multiplied by 9 equals 45. The inverse of this would be 45 divided by 9 equals 5.