Final answer:
Pyonephrosis is the term that refers to pus formation in the kidney.
Step-by-step explanation:
The term that means pus formation in the kidney is pyonephrosis. Pyonephrosis is a severe and rare condition in which there is a collection of pus in the renal pelvis, which is the central part of the kidney. It is usually caused by an obstruction in the urinary system that leads to the accumulation of bacteria and subsequent infection.
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