A mass of blood that forms when blood platelets, proteins, and cells stick together. When a blood clot is attached to the wall of a blood vessel, it is called a thrombus. When it moves through the bloodstream and blocks the flow of blood in another part of the body, it is called an embolus.
Last updated: 2014-02-26
Source: The National Cancer Institute's Dictionary of Cancer Terms (http://www.cancer.gov/dictionary)