Phlebitis is the term used to describe the inflammation of a vein. When the source of that inflammation is a blood clot or thrombus, it becomes thrombophlebitis. Thrombophlebitis can affect both deep and superficial veins.
Superficial phlebitis is more likely to develop in patients that have varicose veins or that have experienced vascular trauma (damage to the blood vessel wall). While superficial thrombophlebitis can be very painful, it is generally not life threatening. Thrombophlebitis in the deep veins is a serious condition and is referred to as deep vein thrombus (DVT).