1. The difference between an exact mathematical value and the value that is approximated during a calculation or computation in which rounding occurs. So many of the values we have to use in these calculations have decimals that extend to an infinite length that rounding errors are simply unavoidable. It may seem like we leave a very large rounding error when we use 3.14159 as the value for pi, but in most instances it will give us a result that it accurate enough for our purposes.

2. A figure that is or seems large in isolation but is relatively small or immaterial to a large company. The settlement of $300,000 is little more than a rounding error to a global corporation that earns billions of dollars each year. I'm nervous about asking for a raise, but I'm trying to tell myself that it is just a rounding error in the company's eyes.