A niche is a special area of expertise or a skill. It may be limited to a small number of people or a small demographic* area. We often hear people finding their niche, which means to discover a talent within oneself.
Abel found his niche as an importer of Peruvian-made jewelry.
Charlene has finally found her niche working in the cosmetics industry.
Xavier is still trying to find his niche. (These three examples show the popularity of using "find" with "niche.")
Many businesses thrive in New York City due to the existence of niche markets not found elsewhere.
Snowboarding, once a niche sport, is now popular wherever there’s snow.
Product placement in movies and television shows has grown from a form of niche advertising to one that is more mainstream.
*demographic: a group of people identifiable by gender, age, race, level of income, interests, geography, etc.