From CS2800 wiki

Octal is another word for base 8. It is useful for the same reasons as hexadecimal notation, although it is less commonly used. Some programming languages allow you to write a number in octal notation by prefixing it with a 0 as in "0172" which (in some contexts) would be interpreted as [math]\href{/cs2800/wiki/index.php/Base}{(0172)}_8 [/math] or [math]122 [/math].