A DVT — deep vein thrombosis — is a blood clot in one of the deep veins, most often in the leg. It matters urgently for one reason: a piece of the clot can travel to the lungs (a pulmonary embolism). Sudden swelling, pain, warmth or colour change in one leg deserves same-day medical care — that sentence is the most important one on this page.
In this community, DVT carries an extra layer: a clot in the left leg — especially in a younger woman, around pregnancy, or without another explanation — is the classic presentation of May-Thurner syndrome, and it's often the event that finally gets the compression diagnosed. If you've had a left-sided DVT and nobody looked at the iliac vein afterwards, that question is still worth asking.
Treatment is anticoagulation ("blood thinners") for a defined period, longer with recurring clots or a clotting tendency (see MTHFR for the gene question everyone asks). Flying and travel precautions come up constantly — short answers in our exercise & movement Q&A.