A histogram is a simple bar graph frequency distribution from which the height represents the frequency, and the position on the X-axis represents the varible. Histograms often form a bell-curve as there is one central median.
Found - http://www.graphicsserver.com/SampleApps/DotNet/General/Chart%20Types/Custom%20Charts/Histogram/Histogram.png
This blog is a map catalog in which I am displaying fifty different types of maps and a tid-bit of information that looks into the purpose of the map!