The mode is the most frequently occurring value in the data and can be used as a measure of central tendency for categorical data.
The mode of a variable $X = \lbrace x_{1},...,x_{n} \rbrace $ is a measure of central tendency and is given by the most frequent occurring value in the data set. For example, for realizations of $X = \lbrace 2, 2, 2, 3, 3, 4, 5 \rbrace $ the mode is 2, whereas the median is 3 and the mean is 2.57. The mode is the value for $X = x$ at which the probability mass/density function of $X$ has its peak.
Note that the mode is a poor measure of central tendency if the most frequent value in the data is not close to the center of the data. The mode also might not necessarily have a unique value as for instance a bimodal distribution has 2 modes. Mean, mode and median coincide in the normal distribution. Another extreme is the uniform distribution where each value is the mode.
