Niche is a small but potentially profitable market segment. A niche has also been known to imply a working position or an area suited to a person who occupies it, basically a job where a person is able to succeed and thrive.

Related term:

Niche marketing is the process of finding and serving small but potentially profitable market segments and designing custom-made products or services for them. For big companies those market segments are often too small in order to serve them profitably as they often lack economies of scale.