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.
|1991 - 92||10||10|
|1992 - 94||15||10 + 15 = 25|
|1994 - 96||9||25 + 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.