Acetone: In the body, a chemical that is formed when the body uses fat instead of glucose (sugar) for energy. The formation of acetone means that cells lack insulin or cannot effectively use available insulin to burn glucose for energy. Acetone passes through the body into the urine as one of the so-called ketone bodies.

Acetone is highly volatile. The breath of someone with a great deal of acetone in the body smells fruity and is called "acetone breath."