Deep leg veins (the light blue veins in the picture) include the iliac, femoral, popliteal, and tibial veins. Superficial leg veins (the dark blue veins) include the greater and lesser saphenous veins.

In deep vein thrombosis, a blood clot (thrombus) forms in a deep vein, usually in the legs. Clots also can form in superficial veins, which are closer to the skin.