Source : Free On-Line Dictionary of Computing

logical complement
     
         In {Boolean algebra}, the logical complement or
        negation of a Boolean value is the opposite value, given by
        the following {truth table}:
     
        	A | -A
        	--+---
        	T | F
        	F | T
     
        -A is also written as A with a bar over it or with a small
        vertical line hanging from the right-hand end of the "-"
        ({LaTeX} \neg) or as A'.  In the {C} programming language, it
        is !A and in digital circuit design, /A.
     
        (1995-01-24)