Graph
From GDWiki
A graph is a basic mathematic concept meaning a collection of points with lines between them. Graphs can have diverse meanings, but a common use of them is to represent points in space and the connections between them. If you take a number of cities near you as the points (nodes), and the important roads between them as the lines, you've got a graph. There is also such a thing as a weighted graph, where each line has a 'weight' attached to it (in the previous example this would be the length of the road).
Graphs may sound simple, but there's a whole field of mathematics associated with them. There are many neat (and some actually useful) tricks you can do with them. See A* for an example.
Below is a simple graph:
Below is an example of a weighted graph:
An example of a weighted graph
And above here is an example of a weighted graph. Note that the weights are arbitrary, they do not have to adhere to a certain scale or rule. The weights between points in the graph may have any meaning necessary. It could be a measure of distance, a measure of time, the average number of african swallows that travel between these cities in a given eon, etc. The weights only matter in the mathematical algorithm that is applied to the graph, such as in Dijkstra's Algorithm.
