Lilium is a genus of herbaceous flowering plants growing from bulbs, all with large and often prominent flowers. They are the true lilies. Lilies are a group of flowering plants which are important in culture and literature in much of the world. Most species are native to the Northern Hemisphere and their range is temperate climates and extends into the subtropics. Many other plants have "lily" in their common names, but do not belong to the same genus and are therefore not true lilies.

In botany, a bulb is a short underground stem with fleshy leaves or leaf bases that function as food storage organs during dormancy. In gardening, plants with other kinds of storage organ are also called ornamental bulbous plants or just bulbs.