What does it mean to have plaque in the arteries?

Some researchers believe that the initial cause for atheroslerosis stems from some type of bodily response to injury: such as damage to the tunica intima (of the blood vessel) caused by ingestation of poison, hypertension, a bacterial infection, or even damage caused by a physical blow. The irritated endothelium of the blood vessel sets off the body's reactions to repair the damage, which results in clotting and a patch formation of plaque. Visualize how your body forms a scab on your knee, but this process is happening inside of your body within a very small blood vessel (artery). How this plaque may continue to grow is a multi-step process involving many factors such as endothelial cells, chemotactic agents, growth factors, lipoproteins, etc. However, fibrous plaque (athero lesions) is the buildup of collagen and elastin fibers which thickens the tunica intima (innermost lining of the blood vessel). You can look up "atherosclerosis" for more detailed information.