Abscissa and ordinate is the distance between the projection and the origin of the axis, and whose sign is given by the location on the projection relative to the origin (before: negative; after: positive). Usually these are the horizontal and vertical coordinates of a point in a two-dimensional rectangular Cartesian coordinate system. The terms can also refer to the horizontal and vertical axes respectively (typically "x"-axis and "y"–axis) of a two-dimensional graph. An ordered pair consists of two terms—the abscissa (horizontal, usually "x") and the ordinate (vertical, usually "y")—which define the location of a point in two-dimensional rectangular space. Though the word "abscissa"
Line graph of a hypergraph graph.). In hypergraph theory, it is often natural to require that hypergraphs be "k"-uniform. Every graph is the line graph of some hypergraph, but, given a fixed edge size "k", not every graph is a line graph of some "k"-uniform hypergraph. A main problem is to characterize those that are, for each "k" ≥ 3. A hypergraph is linear if each pair of hyperedges intersects in at most one vertex. Every graph is the line graph, not only of some hypergraph, but of some linear hypergraph . characterized line graphs of graphs by a list of 9 forbidden induced subgraphs.