It's the difference between the decimal value and the binary prefix.
In this case, it's saying you are using 0 binary bytes.
What's the difference?
Using "Giga" as our example, it means 10003 of something (i.e. Gigahertz).
In computers it poses an interesting problem:
A Gigabyte is 10003 bytes. However a byte is 8 (binary) bits. Which means it's technically 10243 bytes. To account for this, we use different notation:
- Giga is decimal (base 10)
- Gibi is binary (base 2)
The output is telling you that it's using binary units.
If you want to get the output in "human readable decimal notation", use a capital "H":
$ df -H
/dev/disk2 1.1T 413G 706G 37% 100935848 172431606 37%
map auto_home 0B 0B 0B 100% 0 0 100% /home
Finally, it's actually not an Apple convention, but one from BSD (it's a BSD command). You can find more info on the man page (