Octal is not commonly used. There are eight digits in this system 0 to 7. Similar to the decimal and binary systems, a number can be broken down into its powers of 8. For example the octal number 345 is equivalent to 229 decimal.
A binary number can be converted into its octal equivalent by breaking it into groups of three. For example, the six digit binary number 111111 (63 decimal) can be converted to octal like so.