Lemon is a fragrant, tart citrus fruit with a bright yellow oval shape and thick, pebbled skin. Lemons are high in Vitamin C and flavonoids, which are antioxidants that improve health and well-being in a variety of ways. Lemon is a fruit that can be used in a variety of ways. It's well-known in the culinary world for its tangy, refreshing flavor, as well as for its natural healing and purifying effects.