1. A tumor or focal excess of elastic tissue fibers or abnormal collagen fibers of the skin.
2. An abnormality in quality or quantity of either cutaneous collagen or elastic fibers in the dermis.
3. A chronic disease of the skin; pseudoxanthoma (a condition resembling xanthoma).

Xanthoma consists of yellowish firm nodules in the skin frequently indicating underlying disease; such as, diabetes, disorder of fats (lipid disorder or hyperlipidemia), or other conditions. A xanthoma is a kind of harmless growth of tissue.

Under the microscope, a xanthoma can be seen to be composed of lipid-laden foam cells. These cells, termed histiocytes, contain lipid material in their cytoplasm (the nonnuclear zone of the cell).

The word xanthoma is made up of xanth- from the Greek roots xanthos, "yellow" and oma, "swelling" which equals "a yellow swelling". A xanthoma is a circumscribed yellow swelling or a "yellowish nodule".