A histogram is a graph of a dataset, composed of a series of rectangles. The width of these rectangles is proportional to the range of values in a class or bin, all bins being the same width. For example, values lying between 1 and 3, between 3 and 5, etc. The height of the rectangles is proportional to the frequency or the relative frequency of that class. For example the height of the bar centered at 2 is determined by the number of values in the class from 1-3.