Bell peppers, or sweet peppers, are a mild cultivar group of Capsicum annuum -- the same species as many chili peppers, but bred without capsaicin, so they carry no heat. They originated in Central and South America and spread worldwide after European contact with the Americas; major producers today include China, Mexico, Spain, and the United States.
Peppers are typically picked green while unripe or left on the plant to ripen into red, yellow, orange, or purple, becoming sweeter as they ripen. Crisp and mild, they're a staple across Mediterranean, Latin American, and Asian cooking -- sautéed, stir-fried, roasted, stuffed, or eaten raw -- and pair readily with onion, garlic, tomato, and most proteins.
The label green pepper is ambiguous across recipes and regions; it does not always mean bell pepper.