Enuresis is defined as:

Enuresis specifically refers to the involuntary discharge of urine, particularly occurring during sleep. This condition is most commonly recognized as bedwetting in children, but can also apply to adults. The definition highlights that the involuntary urination happens at night, distinguishing it from other forms of urinary incontinence that may occur during the daytime.

Other options suggest different conditions. For instance, urinary incontinence during the day is a different classification and would not be termed enuresis. A loss of appetite pertains to nutrition and feeding, while frequent urination without control generally relates to conditions like urgency or urge incontinence, which do not specifically refer to the aspect of nighttime bedwetting that enuresis signifies. Therefore, the correct choice aligns with the established definition of enuresis, emphasizing its nighttime occurrence.