An order of magnitude refers to a range designated by a common power of ten: tens, hundreds, thousands, millions, hundred billions, etc.
Orders of magnitude are used in comparisons, especially in science. Two quantities are said to be on the same order of magnitude if they are within a factor of ten of each other. For example, the area of the United States and that of China are of the same order of magnitude. The length of an centimeter and the length of a mile differ by a factor of 5280 × 12 × 2.54 = 160934.4, so those quantities differ by five orders of magnitude (105).