A statistician's fancy name for percentage or proportion. In a population, the relative frequency of a discrete variable is the number of items in that category, divided by the number of items in the population. For continuous variables one can establish the relative frequency of an interval by integrating the variable over the interval and dividing by the integral of the variable over the entire range.

Obviously must be between zero and one.

A histogram is a chart of relative frequency with respect to category or interval. A pie chart is another way of displaying relative frequency. Other charts are just more complicated versions of this. A good histogram will have relative frequency proportional to the area of the bar, not the height — area is easier for people to compare than length.

|    ***  |
|*** ***  |***
|*** ***  |***  ******
|*** ***  |***  ******
+-------- +-----------
 1-2 3-8   1-2  3 - 8

Also, the width of the bar should be proportional to the length of the interval, as the above graphs show. These cautions prevent the use of statistics for its proscribed purpose — that is, lying.