What is the difference between graph and chart?

Basically, there are many different types of chart. A graph is just one of thse types.

Have a look here. http://en.wikipedia.org/wiki/Chart

In my experience, the word 'diagram' is a lot more common than the word 'chart'.

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As per the earlier answer, the major classification under Chart could be "data driven graphs" (based on numerical values) and "conceptuals" (visual layout derived from a set of text on the basis of some logic e.g., org chart, Pyramid layout, RoIC tree and so on.

me confused
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Surely this isn't true. There used to be line graphs, bar graphs etc. Somehow chart has superceded graph.

Diagrams are something else again.