In the SI measurement system, the metric prefix for 10^6 is "mega-." This prefix stands for one million, which is expressed as the power 10^6. The symbol for "mega-" is M.
In the metric system, there are 20 SI prefixes used to express either very small or large values. For example, the prefix "yotta" represents one septillion. Expressed in powers of 10, this is equivalent to 10^24.
Metric prefixes precede a unit of measure to denote a multiple of the unit. Some examples of using prefixes for different units of measurements are megameter, millimeter and kilogram. The meter is a unit of length, and megameter and millimeter denote multiples of this length. While a megameter is one million meters, a millimeter is 1/1,000th of a meter. Similarly, the gram is a unit of mass. Because the prefix "kilo-" denotes a factor of 1,000, 1 kilogram is 1,000 grams.