A niche is a space that's all your own, from a literal corner or enclosure to some kind of professional specialty. Like finding a niche in the scented soaps market with peanut butter body wash and winning over a loyal, if not nutty, following.
In the 1600s, niche was first recorded as meaning a “shallow recess in a wall." The figurative sense of the word didn’t come about for another century. So today, you can use niche literally to refer to a cranny or crevice, or figuratively to talk about an activity or role in life that is particularly suited a person’s interests or talents. Synonyms range from alcove and compartment to nook and opening.