<P> In graph theory, a loop (also called a self - loop or a "buckle") is an edge that connects a vertex to itself . A simple graph contains no loops . </P> <P> Depending on the context, a graph or a multigraph may be defined so as to either allow or disallow the presence of loops (often in concert with allowing or disallowing multiple edges between the same vertices): </P>

An edge of a graph that joins a vertex to itself is called a