Oedema (U.S. edema) is dropsy. It was usually called dropsy until about the middle of the 20th century.
It is a medical condition, and a sign or symptom. It is swelling caused when fluid leaks out of the body's capillaries into the tissues. The fluid builds up and gets trapped in the tissues around the leaking blood vessels. This causes swelling. If there is enough swelling, oedema can be seen from outside of the skin.