The mode is the most common value in a dataset.

A distribution of values with only one mode is called unimodal.
A distribution of values with two modes is called bimodal.
In general, a distribution with more than one mode is called multimodal.

The mode can be found for both categorical and numerical data.

Numerical example:
4, 7, 3, 8, 11, 7, 10, 19, 6, 9, 12, 12
The modes of this dataset are both 7 and 12.

Categorical example:
Alice, John, Bob, Maria, John, Julia, Carol
John is the mode of this data.

In Python, the mode can be found with the multimode() method:

from statistics import multimode  
values = [4,7,3,8,11,7,10,19,6,9,12,12]  
x = multimode(values)