Source : WordNet®

octal
     adj : of or pertaining to a number system having 8 as its base;
           "an octal digit"

Source : Free On-Line Dictionary of Computing

octal
     
         Base 8.  A number representation using the
        digits 0-7 only, with the right-most digit counting ones, the
        next counting multiples of 8, then 8^2 = 64, etc.  For
        example, octal 177 is digital 127:
     
        	digit    weight        value
        	  1     8^2 = 64   1* 64 = 64
        	  7     8^1 =  8   7*  8 = 56
        	  7     8^0 =  1   7*  1 =  7
        			          ---
        				  127
     
        Octal system used to be widespread back when many computers
        used 6-bit {bytes}, as a 6-bit byte can be conveniently
        written as a two-digit octal number.  Since nowadays a byte is
        almost always 8-bit long the octal system lost most of its
        appeal to the {hexadecimal} system.
     
        For a brief discussion on the word `octal' see {hexadecimal}.
     
        (1997-06-16)