Octal (pronounced AHK-tuhl , from Latin octo or "eight") is a term that describes a base-8 number system. An octal number system consists of eight single-digit numbers: 0, 1, 2, 3, 4, 5, 6, and 7. The number after 7 is 10. The number after 17 is 20 and so forth.
In computer programming, the octal equivalent of a binary number is sometimes used to represent it because it is shorter.