An inflammation of the vein that causes blood clots to form is called

Actually it is called phlebitis medically which means that the vein is inflammated, Hence this causes the one or more blood clots to form thrombophlebitis, which commonly occurs in leg veins, and also sometimes in arm, which causes the severe pain and irritations, which may lead to blocking of flow of blood in veins.

Generally travels west to east but often shifts to north and south