The histogram comprises a series of bars of uniform width, each one representing the frequency associated with a particular class interval. As with the bar chart, either absolute or relative frequencies may be used on the vertical axis of a histogram, as long as the axis is labeled accordingly.

Unlike the bar chart, the bars of a histogram are contiguous—their boundaries touch—to capture the quantitative nature of the data. (The exception occurs when an ordinal variable is graphed). Values along the horizontal axis, the class intervals, are ordered left to right from the smallest to the largest.

The histogram also communicates the underlying shape of the distribution— ex: more scores at the upper end, fewer at the lower end. Although the latter observation also can be made from Table, such observations are more immediate with a well constructed histogram.

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 Sources:
Fundamentals of Statistical reasoning in Education, Theodore Coladarci, Casey D. Cobb, Edward W. Minium and Robert C. Clarke (Click for eBook)