Generally, the word Cumulative means "how much so far". In statistics, it is the running total of all frequencies. Cumulative frequency corresponding to a particular value is the sum of all the frequencies up to and including that value.

For example, the below cumulative frequency table displays the valconic eruption between 1991 to 2000.

Years           Frequency            Cumulative Frequency       
1991 - 92   10  10
 1992 - 94  15 10 + 15 = 25
 1994 - 96  925 + 9 = 34
 1996 - 98  13 34 + 13 = 47
 1998 - 2000  7 47 + 7 = 54

From the table, the cumulative frequency for the total number of valconic eruption that took place between the years 1994 to 1998 is 34 + 13 = 47. The cumulative frequency is mostly used while analyzing the data, where the value of the cumulative frequency represents the number of samples in the data, that lie below the current value. It is also useful while displaying the data using the histograms.

The Cumulative Frequency can be clearly understood when displayed in a table. A table displaying the cumulative frequencies is called as cumulative frequency distribution and this is one of important type of frequency distribution.

There are main two types of cumulative frequency distribution as follows:

Less than cumulative frequency distribution:
Here, the Cumulative total of the frequencies are obtained by adding frequencies of lowest size to the highest size.

For example:
          
Marks of students             
Less than Cumulative frequency       
Less than 20 7
 Less than 30 
8
Less than 40 12
Less than 50  16
Less than 60  24
Less than 70  37
Less than 80  45
Less than 90  58
 Less than 100  65

From the table, we get to know that student scoring less than 50 is 16.  

More than cumulative frequency distribution:

Here, the Cumulative total of the frequencies are obtained by adding frequencies of the highest size to lowest size.

Marks of students             
  More than Cumulative frequency      
 More than 10  88
 More than 20  74
 More than 30  65
 More than 40  60
 More than 50  58
 More than 60  50
  More than  70  47
 More than 80  29
 More than 90  11

From the table, we can say that the student scoring marks between 40 and 50 is 2
ie, 60 - 58 = 2.