When Euler invented the first graph, he was trying to solve a very specific problem of the citizens of Königsberg, with a very specific representation/model and a very specific algorithm. It turns out that there are quite a few problems that can be addressed as follows:

- Described using the graph metaphor of objects and pairwise relations between them
- Solved by applying a mathematical algorithm to this structure

The mechanism is the same, and the scientific discipline that studies these modeling and solution patterns, using graphs is often referred to as the graph theory and is considered to be a part of discrete mathematics.

There are lots of different types of graphs that have been analyzed in this ...