A 3-coloring of Graph Edges so that no two Edges of the same color meet at a Vertex (Ball and Coxeter 1987, pp. 265-266).
See also Edge (Graph), Tait Cycle, Vertex (Graph)
Ball, W. W. R. and Coxeter, H. S. M. Mathematical Recreations and Essays, 13th ed. New York: Dover, 1987.