What condition describes the formation of kidney stones?

The term that describes the formation of kidney stones is "lithiasis." This term specifically refers to the condition where stones, or calculi, form in the urinary tract, including the kidneys. The formation occurs due to the crystallization of minerals and salts in urine, which can lead to significant pain and obstruction if the stones move through the urinary system.

Understanding the other terms provides context for why "lithiasis" is the correct choice. "Nephritis" refers to inflammation of the kidneys, which is a different pathogenic process altogether. "Cholelithiasis" pertains to the formation of gallstones in the gallbladder, not kidney stones, indicating a distinction between two separate organ systems. "Ureteritis" refers to inflammation of the ureter, which may occur due to other underlying conditions but does not describe the formation of stones. Thus, "lithiasis" accurately encapsulates the specific condition of kidney stone formation.