Medical/anatomical term; in everyday language, 腎臓 (じんぞう) is more common.
See also: 腎臓
I'm worried about the decline in kidney function.
We are looking for a kidney transplant donor.
adrenal gland; suprarenal gland
renal pelvis
right kidney
left kidney
Standard kanji form; often used in medical contexts and compounds.
From Middle Chinese 腎 (dzyinX). The kanji is used in medical terminology for the kidney.