Final answer:
Oliguria is defined as urine production of less than or equal to 400-500 mL per day and is a sign of potential medical issues such as dehydration or renal disease.
Step-by-step explanation:
Oliguria is a condition where the excretion of urine is significantly reduced. It is specifically defined as the production of ≤ 400-500 mL of urine per day. Oliguria can be a sign of various medical conditions including fever, shock, vomiting, and diarrhea, and it indicates inadequate urine output that can be due to severe dehydration or renal disease. In contrast, an anuric condition, where there is no urine excretion or it is below 10 mL/day, is observed in more severe cases such as acute renal failure and nephritis. Notably, the minimum urine volume necessary to maintain normal bodily function and waste removal is about 500 mL/day.