The word "class" has many specialized meanings in mathematics in which it refers to a group of objects with some common property (e.g., characteristic class or conjugacy class.)
In statistics, a class is a grouping of values by which data is binned for computation of a frequency distribution (Kenney and Keeping 1962, p. 14). The range of values of a given class is called a class interval, the boundaries of an interval are called class limits, and the middle of a class interval is called the class mark.
The following table summarizes the classes illustrated in the histogram above for an example data set.
| class interval | class mark | absolute frequency | relative frequency | cumulative absolute frequency | relative cumulative frequency |
| 0.00- 9.99 | 5 | 1 | 0.01 | 1 | 0.01 |
| 10.00-19.99 | 15 | 3 | 0.03 | 4 | 0.04 |
| 20.00-29.99 | 25 | 8 | 0.08 | 12 | 0.12 |
| 30.00-39.99 | 35 | 18 | 0.18 | 30 | 0.30 |
| 40.00-49.99 | 45 | 24 | 0.24 | 54 | 0.54 |
| 50.00-59.99 | 55 | 22 | 0.22 | 76 | 0.76 |
| 60.00-69.99 | 65 | 15 | 0.15 | 91 | 0.91 |
| 70.00-79.99 | 75 | 8 | 0.08 | 99 | 0.99 |
| 80.00-89.99 | 85 | 0 | 0.00 | 99 | 0.99 |
| 90.00-99.99 | 95 | 1 | 0.01 | 100 | 1.00 |
