A plug, composed of a detached blood clot, mass of bacteria, or other foreign body, blocking a vessel.

A thrombus that travels from the blood vessel or heart to another location in the body is called an embolus. The disorder is called an embolism. For example, an embolus that occurs in the lungs is called a pulmonary embolism.
Sometimes other materials can act like an embolus and block blood flow, including:
• Air
• Amniotic fluid
• A piece of atherosclerotic plaque
• Fat clumps
• Small pieces of tumor