The three layers of the artery wall are the innermost tunica intima, the outermost tunica admentita and the tunica media in between them. The tunica intima and the tunica admentita are both highly elastic, with the outer tunica admentita being the tougher of the two and rich in proteins. In arteries, the tunica media is a thick layer mostly composed of smooth muscle and elastic fibers.
The arteries are blood vessels under a large amount of pressure. They receive the output of the pumping heart. This is why they are so heavily reinforced with a thick layer of muscle and two layers of tough, elastic tissue. This stands in contrast to veins, which suffer much lower pressure, even having valves to keep blood flowing in the right direction. The layers of arteries are basically the same as veins, but the tunica media in veins is much thinner.
The term "artery" refers to any blood vessel carrying blood away from the heart. This means that the majority of arteries, the systemic arteries, carry oxygenated blood throughout the body. The pulmonary arteries, however, carry deoxygenated blood to the lungs. Conversely, while most veins carry deoxygenated blood from the body to the heart, the pulmonary veins carry oxygenated blood from the lungs to the heart.