Mind mapping is a very diffused graphical organization technique, and somehow related to concept maps and semantic networks. 

It is one of the standardized graphical techniques: precisely  Buzan, that coined the term at the end of the 60's, describes it this way

"... a mind map consists of a main word or idea; around that word are associated 5 - 10 main ideas related to that term. Once again to every one of these terms are associated 5 - 10 words related to that term. To every one of these descending words so many others may be associated".

In published papers and in social practice, mind maps are also traditionally known as:

"Word maps",
"Idea maps",
"Clusters".

It is common experience to many of us to have used this technique, without knowing that we were using... mind maps.

The terms "mind map", "concept map" and "semantic network" are often used indistinctly but, because these terms are standardized, each one of these techniques has a formal definition that clarifies its features and scopes. Sometimes they are also trademarks of different software products, and therefore it is convenient to make clear references. 

These are different techniques each one with, different capabilities, different scopes, different uses and different semantic power.

Substantially, mind maps are strictly tree structures. As for their typical rigid hierarchical structure, the mind map presents a strictly hierarchical ordering of ideas, in which the nature of the relations between ideas is not important.