Final answer:
Nephrolithiasis is the presence of kidney stones, which are solid concretions formed from minerals in the urine and can cause severe pain and potential health complications if they cause obstruction in the urinary tract.
Step-by-step explanation:
The presence of one or more stones in the kidney is known as nephrolithiasis. These kidney stones are solid concretions formed from minerals in the urine. Symptoms can include severe pain, often described as 'loin to groin' or renal colic, and hematuria, where blood is present in the urine. Kidney stones can vary greatly in size and may pass through the urinary tract without causing symptoms if they are small enough.
However, larger stones can cause significant pain, nausea, and vomiting, and may require medical intervention. Nephrolithiasis can cause obstruction in the urinary tract, leading to health complications such as hydronephrosis, which is the enlargement of the kidneys due to the obstruction of urine flow.