I did not know this:
From the perlfunc man page discussion of the pack() function.
Endian-ness is one of those esoteric (or not) computer subjects that makes the internet work (or not). Basically, do you (or more accurately, your computer) count from left-to-right, or right-to-left. Little endian is left-to-right (1234) and big-endian right-to-left (4321).