Following Wikipedia, a niche market is a focused targetable subset of a big market. These are markets that are usually ignored by mainstream providers because niche markets are small.Despite this, niche markets may still become profitable because of the specialization and the identification of you target market. Actually, choosing your niche market may be better for you because you will not have to waste time marketing to people who are not interested in the products you are selling.
Link: Niche market - Wikipedia, the free encyclopedia