Bed-wetting is when someone, most often a child, passes urine in the night while asleep — they wet the bed. It is common in young children and often fades as the body learns to hold on till morning. It is not laziness and not naughtiness; the child is asleep and does not choose it. Kind families treat it as a stage, with a mattress cover and patience, not as a joke. Though actually it is not only a small-child story. Some older children still have it, and some adults do too; doctors may then use a more medical word, enuresis. People also say wet the bed for the action, and bedwetter for the person, but bedwetter can sound unkind, like a label, so careful speakers stay with the problem-name bed-wetting. The hyphenated form is the usual dictionary spelling; you will also see bedwetting written as one word.