A reversible function is a type of mathematical function where each output is uniquely associated with one input. This means that if you know the output, you can determine the original input. In simpler terms, a reversible function can be "undone" or reversed, allowing you to go back to the starting point. An example of a reversible function is the addition of a number. If you add 5 to 3 to get 8, you can easily reverse it by subtracting 5 from 8 to return to 3. In contrast, non-reversible functions, like squaring a number, do not allow for a unique reverse since both -2 and 2 yield the same result, 4.