Hemodialysis: A medical procedure that uses a special machine (a dialysis machine) to filter waste products from the blood and to restore normal constituents to it. This shuffling of multiple substances is accomplished by virtue of the differences in the rates of their diffusion through a semipermeable membrane (a dialysis membrane).
Although hemodialysis may be done for acute kidney failure, it is more often employed for chronic renal disease. Hemodialysis is frequently done to treat end-stage kidney disease. Under such circumstances, kidney dialysis is typically administered using a fixed schedule of three times per week.
There are other types of dialysis as, for example, peritoneal dialysis.