The lymphatic system is a part of the immune system and vital for immune function. 

Lymphedema is fluid that builds up in the arms or legs. As fluid flows through lymph nodes trapping bacteria and other substances, white cells in the bodies defense or immune system can destroy these substances; however, if there are few or no lymph nodes or the lymph system in an arm or leg has been damaged, fluid can build up in the affected arm or leg. In some cases, lymphedema can be caused by genetic mutation or by other conditions such as infections and inflammatory diseases.

The main symptom is swelling (edema) in the arm or leg that may be accompanied by pain or discomfort.