Median graph
In graph theory, a division of mathematics, a median graph is an undirected graph in which every three vertices a {\displaystyle a} , b {\displaystyle b} , and c {\displaystyle c} have a unique median: a vertex m ( a , b , c ) {\displaystyle m(a,b,c)} that belongs to shortest paths between each pair of a {\displaystyle a} , b {\displaystyle b} , and c {\displaystyle c} . The concept of median graphs has long been studied, for instance by Birkhoff & Kiss (1947) or (more explicitly) by Avann (1961), but the first paper to call them "median graphs" appears to be Nebeský (1971).