Thrombosis
The formation or presence of a blood clot in a blood vessel.
The vessel may be any vein or artery as, for example, in a deep vein thrombosis or a coronary (artery) thrombosis.
The clot itself is termed a thrombus.
If the clot breaks loose and travels through the bloodstream, it is a thromboembolism.
Thrombosis, thrombus, and the prefix thrombo- all come from the Greek thrombos meaning a lump or clump, or a curd or clot of milk.
See entries also to: Cavernous sinus thrombosis; Renal vein thrombosis.