Emboli are particles, such as blood clots, fat, air, or other substances, that travel through the bloodstream and obstruct a blood vessel at a site distant from their origin. They are clinically significant because they can cause sudden tissue ischemia or infarction, leading to organ dysfunction or failure. A common and serious example is a pulmonary embolism, where a clot blocks blood flow in the lungs, causing respiratory distress and potentially fatal outcomes.