Which condition involves the secretion of a diminished amount of urine in relation to fluid intake?

The condition that involves the secretion of a diminished amount of urine in relation to fluid intake is characterized by a significantly reduced urine output, typically defined as less than 400 milliliters per day in adults. This condition is known as oliguria. Oliguria can result from various medical issues, such as dehydration, kidney dysfunction, or certain medications, which lead to a reduced capacity of the kidneys to filter and excrete urine.

In contrast, other options address different urinary conditions: renal calculi refer to kidney stones that can cause pain and obstruct urine flow, nocturia involves waking up during the night to urinate, and enuresis refers to involuntary urination, often in children. Thus, the key defining factor of oliguria is the specific decrease in urine production relative to fluid intake, making it the correct choice for this question.