The unset statement isn't actually a function, although it's called like a function. It is used to set parameters of characters, objects, and rooms to "nothing". The argument is the parameter you wish to unset.
Only a few MUDL functions can meaningfully be unset; at the time of this writing, those are target (which stops combat between this character and whomever he is fighting), grappling, worships, and master (which stops the target from following anybody).
Examples:unset( target( %a ) )See also the set statement, which can be used to set things to values other than "nothing".