diagram vs undirected graph

diagram

noun
  • A graph or chart. 

  • A plan, drawing, sketch or outline to show how something works, or show the relationships between the parts of a whole. 

  • A functor from an index category to another category. The objects and morphisms of the index category need not have any internal substance, but rather merely outline the connective structure of at least some part of the diagram's codomain. If the index category is J and the codomain is C, then the diagram is said to be "of type J in C". 

  • Electrical diagrams show device interconnections. 

verb
  • To schedule the operations of a locomotive or train according to a diagram. 

  • To represent or indicate something using a diagram. 

undirected graph

noun
  • A graph in which the edges are not ordered, so the edge (a, b) is identical to the edge (b, a). 

How often have the words diagram and undirected graph occurred in a corpus of books? (source: Google Ngram Viewer )