Wolfram Research
Wolfram Math World: Frequency Distribution
This site from MathWorld provides a general overview of frequency distribution, complete with a bar graph and explanatory text.
Richland Community College
Richland Community College: Stats Graphs Defined
Richland Community College provides a glossary of many terms that are needed in order to understand statistics graphs and charts. Each of the types of charts is quickly explained in terms of what it is most effective in displaying.
University of Illinois
University of Illinois: Spreading It Thick
Resource contains the definition for variance. It also shows students how to calculate the variance. There is a link to a bar graph that displays variance for the data example.