#!/bin/sh is a command in the beginning of a
shell script, sometimes called a
header. The
shell executing the
script checks whatever is behind the #! and executes what follows that line with whatever is on that line. For example, if I want my
script to be run in the
Korn shell i would put #!/bin/
ksh in the beginning of my script.
Also a
vanity IRC channel, something that just looks
cool when someone does a /
whois on you.