In a nutshell, edema simply means "swelling", and while I can give you a variety of symptoms, causes and possible treatments, you should note that an accurate diagnosis cannot be given without having examined the patient and analysed his/her individual circumstances.
Edema, or swelling, occurs when there is too much liquid in your body's tissues and it is unable to escape. Certain medicines can cause edema, and it can also be a symptom of an underlying condition, rather than a condition in itself. These underlying conditions can include cirrhosis of the liver, kidney disease or heart failure, so it is extremely important to obtain an accurate diagnosis.
Mild edema, on the other hand, can be far less serious. It can simply be caused by sitting for too long, such as on a long flight. Pregnancy is another common cause of edema, and it can also be a sign of being premenstrual. In addition, edema can be a side effect of certain medications, including those for the treatment of diabetes and high blood pressure.
The correct treatment of edema will, of course, depend on determining its underlying cause. Mild edema, such as that caused by sitting on a long haul flight, will generally ease off on its own. If medicine is required, diuretics are often prescribed to help the body get rid of excess fluid by turning it into urine.