A graph with vertices that are linked to concepts and edges that represent relations such as "is like" or "includes". Visual Tour function of this WikiWiki shows a portion of the knowledge, the Knowledge Mapping science abbreviates to KM.
An extensive repository of KM topics: http://www.voght.com/cgi-bin/pywiki?KnowledgeMapping
KnowledgeMapsWhitePaper Summary of Collaborative Knowledge Mapping in Business Information Management
See also MindMap, MentalModel