Diagram

                         A diagram is a two-dimension geometric symbolic representation of information according to some visualization technique. 

                         Sometimes, the technique uses a three-dimensional visualization which is then projected onto the two-dimensional surface. The word graph is sometimes used as a synonym for diagram.

Diagrams are information graphics that are made up primarily of geometric shapes such as rectangles, circles, diamonds, or triangles, that are typically (but not always) interconnected by lines or arrows.  

One of the major purposes of a diagram is to show how things, people, ideas, activities, etc. interrelate and interconnect.  

Unlike charts and graphs, diagrams are used to show interrelationships in a qualitative way.