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.)