Source : Free On-Line Dictionary of Computing

least fixed point
     
        A function f may have many {fixed points} (x such that f x =
        x).  For example, any value is a fixed point of the identity
        function, (\ x . x).  If f is {recursive}, we can represent it
        as
     
        	f = fix F
     
        where F is some {higher-order function} and
     
        	fix F = F (fix F).
     
        The standard {denotational semantics} of f is then given by
        the least fixed point of F.  This is the {least upper bound}
        of the infinite sequence (the {ascending Kleene chain})
        obtained by repeatedly applying F to the totally undefined
        value, bottom.  I.e.
     
        	fix F = LUB {bottom, F bottom, F (F bottom), ...}.
     
        The least fixed point is guaranteed to exist for a
        {continuous} function over a {cpo}.