Answer:
Here is a definition from Wikipedia. A mind map is a diagram used to represent words, ideas, tasks, or other items linked to and arranged around a central key word or idea.
Tony Buzan appears to be the first person to come up with the concept of a Mind Map although this is contested. He emphasises the importance of using colour, drawings and images to improve learning and memory. He advocates mind mapping as vastly superior to traditional linear note taking.
See related links for an example mind map.