toggle

toggle vt.  To change a {bit} from whatever state it is
   in to the other state; to change from 1 to 0 or from 0 to 1.  This
   comes from `toggle switches', such as standard light switches,
   though the word `toggle' actually refers to the mechanism that
   keeps the switch in the position to which it is flipped rather than
   to the fact that the switch has two positions.  There are four
   things you can do to a bit: set it (force it to be 1), clear (or
   zero) it, leave it alone, or toggle it.  (Mathematically, one would
   say that there are four distinct boolean-valued functions of one
   boolean argument, but saying that is much less fun than talking
   about toggling bits.)