Source : Free On-Line Dictionary of Computing

transitive closure
     
        The transitive closure R* of a relation R is defined by
     
        	x R y => x R* y
        	x R y  and  y R* z => x R* z
     
        I.e. elements are related by R* if they are related by R
        directly or through some sequence of intermediate related
        elements.
     
        E.g. in graph theory, if R is the relation on nodes "has an
        edge leading to" then the transitive closure of R is the
        relation "has a path of zero or more edges to".  See also
        Reflexive transitive closure.