Decimal is a special expression of real numbers. All fractions can be expressed as decimals, and the points in decimals are called decimal points, which are the dividing lines between the integer part and the decimal part of a decimal. Decimals with zero integer parts are called pure decimals, and decimals with non-zero integer parts are called decimals.

A whole average can be divided into several parts, 100 part, 1000 part ... such 1 part is one tenth, percentage, one thousandth ... such a fraction can be expressed as a decimal. One decimal place indicates a few tenths, two decimal places indicate a few percent, and three decimal places indicate a few thousandths.