Learner's definition of NICHE
a job, activity, etc., that is very suitable for someone
the situation in which a business's products or services can succeed by being sold to a particular kind or group of people
— usually singular
They're still trying to find their niche in the market/industry.
This product fills a niche in the market. = This product fills a market niche. [=provides something that certain kinds of people want to buy]
— often used before another noun
an environment that has all the things that a particular plant or animal needs in order to live
a curved space in a wall that is designed to hold a statue, vase, etc.