a mathematical expression used to represent any decimal number as a number between one and ten raised to a specific power of ten (Ex.: 4.1 × 100 for 4.1, 4.1 × 101 for 41, 4.10 × 102 for 410, 4.1 × 10-1 for 0.41, 4.1 × 10-2 for 0.041): often used for approximate computations with very large or small numbers