A concept map or a mental map (as of now, we'll use the first as a unifying term) is a class diagram that tries to represent graphically a conceptual system components as well as relations between them.
By conceptual system we understand at least two things: (a), any more or less coherent and organized set of ideas within a larger or more complex theory, for example, the theory of evolution; (b), any set of entities and their relationships, for example, firms in a given country.
Conceptual maps do not have any restricted area, so that any aspect of the real world or the conceptual world is likely to be represented in a concept map. The complexity of the system that must be represented either sets any entry restriction: we cannot represent a conceptual map a theory as simple as the regulations governing use of a municipal swimming pool (which does not offend anyone in the world of swimming) or as complex as the one mentioned before
