Here's the official definition from AskOxford.com:
niche/neesh, nitch/
• noun 1 a shallow recess, especially one in a wall to display an ornament. 2 (one’s niche) a comfortable or suitable position in life. 3 a specialized but profitable corner of the market. 4 Ecology a role taken by a type of organism within its community.
— ORIGIN French, ‘recess’, from Latin nidus ‘nest’.
