Repeating decimals are decimal numbers that have either one digit or a group of digits that repeat over and over without ever ending.
For example, as a decimal is
This is a repeating decimal, sometimes known as '0.3 recurring'. To show that a decimal is recurring, you draw a horizontal line over the number or numbers that repeat, such as
All repeating decimals can be rewritten as fractions, meaning that they are rational numbers.
All repeating decimals are rational numbers, and can therefore be turned into fractions. 9 as a denominator has a lot of repeating decimals:
All repeating decimals have a denominator that is a factor of a prime number other than 2 or 5 (3, 7, 11 etc.)