Updated June 09, 2015.

Definition: An area of tissue that receives blood from a single blood vessel or a single group group of blood vessels.

Examples: The internal carotid arteries are two of the main blood vessels that bring blood to the front-half of the brain. The left internal carotid artery brings blood to the left side of the brain, while the right internal carotid artery brings blood to the right side of the brain.

Thus, one can say that the vascular territory of the left internal carotid artery is the left front-half of the brain, while that of the right internal carotid artery is the right half of the brain.