Deep Venous thrombosis and pulmonary thromboembolism Define and classify embolism Embolism: An embolism is defined as any foreign substance that travels through the blood vessels and gets lodged within it leading to blocking of blood flow. The second kinds are those that get lodged in the veins, These are not as severe as arteries but can cause an obstruc?on in the exchange of gases and turn into a third classifica?on known as a pulmonary embolism.