What is an artery classified as tissue or organ?

Artery is an organ.

An artery is a blood vessel that carries oxygenated blood away from the heart to the body's tissues. It has three layers, the tunica intima, the tunica media, and the tunica adventitia. The tunica intima is the innermost layer and consists of a single layer of endothelial cells. The tunica media is the middle layer and consists of smooth muscle cells. The tunica adventitia is the outermost layer and consists of connective tissue. Arteries are classified as organs because they are composed of different types of tissues that work together to perform a specific function.