An unusual retention of lipids by a cell or organ; fatty degeneration; steatopathia: Steatosis is an accumulation of fat in the interstitial (small openings, gaps, or cracks) tissue of an organ.

Steatosis normally affects the liver, known as the "fatty liver" disease. Steatosis can also affect the heart, the kidneys, and the muscles.

Steatosis can lead to impairment of tissues and decreased functioning of the damaged organ.