Final answer:
Kidney stones, known as renal calculi, are mineral crystal aggregations in the urine that can range in size and cause severe pain if they obstruct the urinary tract.
Step-by-step explanation:
Kidney stones are also referred to as renal calculi. They are solid concretions or crystal aggregations formed from dissolved minerals in the urine. When these stones are located within the kidneys, it's known as nephrolithiasis, and when found in the bladder, it's called urolithiasis. Renal calculi can range in size and may pass through the urinary tract without causing symptoms; however, larger stones can cause severe pain, known as renal colic, and may require medical intervention.