The mode is defined as the element that appears most frequently in a given set of elements. Using the definition of frequency given above, mode can also be defined as the element with the largest frequency in a given data set.
The mode or the modal value is that value in a series of observations which occurs with the greatest frequency.
Example: The mode of the series 3, 5, 8, 5, 4, 5, 9, 3 would be 5.
In certain cases there may not be a mode or there may be more than one mode.
Example: (1) 40, 44, 57, 78, 84 (no mode) (2) 3, 4, 5, 5, 4, 2, 1 (modes 4 and 5) (3) 8, 8, 8, 8, 8 (no mode)
For a given data set, there can be more than one mode. Hence, it is called ill defined.