  The field of two-dimensional topological semimetals, which emerged at the
intersection of two-dimensional materials and topological materials, have been
rapidly developing in recent years. In this article, we briefly review the
progress in this field. Our focus is on the basic concepts and notions, in
order to convey a coherent overview of the field. Some material examples are
discussed to illustrate the concepts. We discuss the outstanding problems in
the field that need to be addressed in future research.
