Mode is the most frequent value in a dataset. It may not be unique and a dataset can have more than one mode. It is most insensitive to aberrant values.
For the dataset: 2, 6, 13, 17, 22, 22, the mode is 22.
For the dataset: 2, 6, 13, 17, 22, the mode is either one or none. Therefore, mode may not be unique or available.