Any fruit of a plant of the botanical genus Capsicum, which has a spicy/burning flavour because it contains capsaicin. (Not all chili peppers are particularly spicy, but all true chili peppers contain some capsaicin, in contrast to e.g. the bell pepper, which is not a true chili pepper and does not.)
The fruit of a non-spicy cultivar of pepper, Capsicum annuum, marketed in green-, red-, yellow- and orange-skinned varieties.