A blood clot is a jelly-like mass of congealed blood. But a blood clot within a blood vessel is dangerous and life-threatening. The blockage of blood flow in a vessel is called thrombosis.
Cerebral thrombosis is a blood clot in an artery to the brain, which can cause a stroke.
People with arteriosclerosis are more likely to get blood clots because the inner walls of the blood vessels are rough.