lemon, Small thorny tree or spreading bush (Citrus limon) of the rue (or citrus) family and its edible fruit. Under the yellow outer rind or peel is the white, spongy inner peel, the source of commercial pectin. The juicy pulp is acidic and rich in vitamin C and contains smaller amounts of B vitamins. The climates of coastal Italy and California are especially favourable for the cultivation of lemon trees, which in these regions produce fruit 6–10 times a year. Lemon juice enhances many dishes, and lemonade is a popular warm-weather beverage. Lemon by-products are used in beverages (citric acid), fruit jellies (pectin), and furniture polish (lemon oil).