Bar chart or histogram What's the difference between a bar chart and a histogram?
 A: I disagree with wiki answers, which although it's partially correct, completely misses the main point.  The heights in a bar chart represent counts.  You can use a bar chart for this purpose with categorical data or with binned "continuous" variates; either is fine.  The areas in a histogram represent relative frequencies or proportions per unit value of a continuous variate.  A histogram thus is a discrete approximation to a frequency or probability density function, whereas a bar chart has no such meaning (except accidentally when it's really serving as a histogram!).  The distinction comes to the fore when the bars in a histogram have varying widths.
Reference: Freedman, Pisani, Purves, Statistics.  (Any of the first through fifth editions should be fine.)
A: With bar charts, each column represents a group defined by a categorical variable; and with histograms, each column represents a group defined by a quantitative variable.
See this link: http://wiki.answers.com/Q/What_is_the_difference_between_Bar_chart_and_a_frequency_histogram
