A niche is a space into which something fits. The word is often used in reference to ecology, but it can also reference a person's specialty.
Niche comes from the Old French word "nichier" which means to nest. In architecture, a niche is a decorative inset area in a wall that can be used to display statues or other collectibles. When used in relation to ecology, a niche is the place in which a specific species fits into its environment. Niche may also refer to a segment of the population. When people find their place in the world, it is often said they have found their niche.