A concentration is similar to what is called a minor by other schools within the university (such as SEAS). Effectively, a concentration has more requirements than a minor, but fewer than a major. In Columbia College, a concentration is enough for graduation, or it can be paired with another concentration or with a major.
Columbia College currently lists two special concentrations, linguistics and sustainable development. These concentrations cannot stand alone and must be paired with another concentration or major in order to graduate. The reasoning given by Academic Affairs is that there is not enough full-time staff teaching in these departments to merit a full concentration.