Two-thirds expressed as a decimal is 0.6, with a line over or under the six, indicating that the six repeats indefinitely, or as 0.666, which is accurate to three decimals. To convert a fraction to a decimal, divide the numerator, the top number, by the denominator, the bottom number.
When divided as such, some fractions come out even and are called "terminating decimals." There are no repeating figures in terminating decimals. Other numbers, such as 2/3, are called "recurring decimals." When dividing 2/3, the division does not work out as an even number, so the six is repeated to infinity.