Lettuce (Lactuca sativa) is an annual plant of the daisy family, Asteraceae. It is most often grown as a leaf vegetable, but sometimes for its stem and seeds. Lettuce was originally farmed by the ancient Egyptians, who transformed it from a plant whose seeds were used to create oil into an important food crop raised for its succulent leaves and oil-rich seeds. Lettuce spread to the Greeks and Romans; the latter gave it the name Lactuca, from which the English lettuce is derived.
In everyday usage, a vegetable is any part of a plant that humans consume as part of a savory meal.
The term "vegetable" is somewhat arbitrary and largely defined through culinary and cultural tradition. It normally excludes other food derived from fruits, nuts, and cereal grains, including seeds such as pulses.