What does "dialysis" mean and what are the two types?

Dialysis means the separation of substances through a semipermeable membrane, from dia meaning through and lysis meaning loosening or dissolution. In medicine, it refers to the artificial process of filtering waste products and excess fluid from the blood when the kidneys can no longer perform this function. Hemodialysis filters blood through an external machine, typically three times per week. Peritoneal dialysis uses the patient's own peritoneal membrane as the filter by instilling fluid into the abdominal cavity. Both types perform the essential filtering function of failed kidneys.