Dialysis: The process of removing waste products and excess fluid from the body. Dialysis is necessary when the kidneys are not able to adequately filter the blood. Dialysis allows patients with kidney failure a chance to live productive lives. There are two types of dialysis: hemodialysis and peritoneal dialysis. Each type of dialysis has advantages and disadvantages. Patients can usually choose the type of long term dialysis that best matches their needs.