Edema - a terminology used to denote swelling. It usually occurs because of - 1.) Inflammation, and 2.) Fluid retention, 3.) Blockage of any major vein and lymph passage. Edema / swelling due to inflammation may occur after trauma, infection and may develop over any part of the body. Edema due to fluid retention (water retention) tends to accumulate in dependent areas - legs, lower back (when in lying down position), eyelids and face (on waking up in the morning).