Base 8 (or
octal) is a number system with only the
digits from 0 to 7. It is (or used to be) useful in
computing/
digital systems, because each digit is represented by exactly three
bits, or three digits of
base 2.
Binary  Octal  Decimal

0000  0  0
0001  1  1
0010  2  2
0011  3  3
0100  4  4
0101  5  5
0110  6  6
0111  7  7
1000  10  8
1001  11  9
1010  12  10
1011  13  11
1100  14  12
1101  15  13
1110  16  14
1111  17  15
Thus, it is easy to convert numbers between binary and octal, simply convert three and three bits. Example: 1000110110_{(2)} = 1 ; 000 ; 110 ; 110_{(2)} = 1066_{(8)}
See also hexadecimal for a similar explanation of base 16.
"Base 8 is just like base 10, really. If you're missing two fingers!"

Tom Lehrer