Process by which a number is approximated to the nearest above or below with one or more fewer decimal places. For example, 34.3583 might be rounded to 34.358, whereas 34.3587 would be rounded to 34.359. Similarly, 3,587 might be rounded to the nearest thousand, giving 4,000. When unwanted decimals are simply left out, the process is known as truncating.
Rounding can produce considerable errors, especially when the rounded numbers are multiplied by other rounded numbers. For example, if the volume of a cuboid is calculated as 3 x 4 x 5 when the true dimensions are 3.4 x 4.4 x 5.4, the rounding error is 20.784 out of 80.784, an error of over 25%.