Final answer:
A benign tumor composed of fat cells is called a Lipoma, which is a non-cancerous mass that typically does not invade other tissues or metastasize.
Step-by-step explanation:
The term used for a benign tumor composed of fat cells is Lipoma. A lipoma is a non-cancerous growth of fat cells that forms a lump beneath the skin. It is usually soft and painless and can occur anywhere on the body where fat cells are present. A lipoma is a type of benign neoplasm or benign tumor which means it is not cancerous, does not invade other tissues, and does not form metastases. It is essentially a growth of fat cells in a thin, fibrous capsule usually found just below the skin. Lipomas are typically removed for comfort or if there is a concern they might become more serious, even though this is quite rare.