Exudate: A fluid rich in protein and cellular elements that oozes out of blood vessels due to inflammation and is deposited in nearby tissues. The altered permeability of blood vessels permits the passage of large molecules and solid matter through their walls. The vessels seem to weep, to sweat, in keeping with the Latin "exsudare", to sweat out, from which exudate is derived.
By comparison, a transudate is a fluid that passes through a membrane which filters out much of the protein and cellular elements and yields a watery solution. The process of transudatation is due to increased pressure in the veins and capillaries pressure forcing fluid through the vessel walls or low levels of protein in the serum. The transudate is a filtrate of blood.