A lipoma is a benign lump or mass that is made up of fat cells (adipocytes). Lipomas are a common, benign (noncancerous) type of slow-growing tumor and are the most common benign tumors situated under the skin.ess commonly, lipomas can grow on almost any organ in the body. Lipomas generally develop slowly, forming round, flattened lumps that are soft or spongy in texture and easily moved around under the skin. Lipomas can be unsightly, but they usually do not cause any pain, discomfort or tenderness.