What is the medical term meaning expansion of a blood vessel?

The medical term meaning expansion or widening of a blood vessel is vasodilation or vasodilatation. It refers to the process by which the diameter of a blood vessel (artery or vein) increases, resulting in an increase in blood flow to a particular tissue or organ. Vasodilation can occur as a normal physiological response to certain conditions, such as increased tissue metabolism, exercise, or in response to certain substances like nitric oxide. It can also be caused by certain medications or medical conditions that affect the tone or control of blood vessels.