(noun)
a position or status, such as a job, activity, or mode of life, that one feels is best suited to them and in which one feels the most comfortable;
e.g. She feels that she hasn't found her niche yet in terms of her career.
(noun)
a section of a market that is specialized or best suited for selling a particular product or service;
e.g. Once the company found a niche for its new product, it could target its advertising to that group.
(noun)
(ecology) the role or position occupied by a particular organism in a specific habitat;
e.g. An animal will occupy a niche in its community based on its food source and the predators that target it.
(noun)
a shallow indentation, or other sheltered space in a wall, especially for displaying an ornament like a statue;
e.g. There was a small candle burning in each niche in the wall.
(adjective)
narrow and specialized in appeal, describing an interest, product, or service;
e.g. He developed a niche interest in medieval European textiles.