A niche market, in marketing terms, refers to a particular segment of the population that has an interest in, love of and desire to spend money on goods and services for something.  It can be anything from a broad niche market like dog breeding to a more specific niche within that niche market, like breeding toy poodles. Having an online business that caters to a niche can be profitable if you pick a niche where people are willing to spend their money.