Real Dictionary

niche
countable noun: A niche in the market is a specific area of marketing which has its own particular requirements, customers, and products.

niche in American English
a recess or hollow in a wall, as for a statue, bust, or vase
to place in or as in a niche
adjective: pertaining to or intended for a market niche; having specific appeal
noun: an ornamental recess in a wall or the like, usually semicircular in plan and arched, as for a statue or other decorative object
transitive verb: to place (something) in a niche

niche in British English
noun: a recess in a wall, esp one that contains a statue
verb: to place (a statue) in a niche; ensconce (oneself)

niche in Retail
adjective: Niche is used to describe products that appeal to a small, limited, or specialized group.