“Graphs* come in a wide variety of different sorts**. The most common type is graphs in which at most one edge* (i.e., either one edge or no edges) may connect any two vertices*. Such graphs are called simple graphs. If multiple edges are allowed between vertices, the graph is known as a multigraph***. Vertices are usually not allowed to be self-connected, but this restriction is sometimes relaxed to allow such “graph loops.” A graph that may contain multiple edges and graph loops is called a pseudograph” (“Graph,” WolframMathWorld, retrieved 6/25/2020, including the picture).
.
*What is the Gist of a “Graph” (Graph Theory)?
**The Wikipedia page called “Graphs” contains a section describing many other types beyond those shown here (retrieved 6/25/2020).
***This is the general rule. However, according to “Multigraph,” from WolframMathWorld, there can be a lot of ambiguity in what is and isn’t required for a graph to be a multigraph.
.
Disclaimer:
I am not a professional in this field, nor do I claim to know all of the jargon that is typically used in this field. I am not summarizing my sources; I simply read from a variety of websites until I feel like I understand enough about a topic to move on to what I actually wanted to learn. By definition, none of these posts address every aspect of a topic. If I am inaccurate in what I say or you know a better, simpler way to explain a concept, I would be happy to hear from you :).
