If you’re really tired during the day, go ahead and take a nap, even if you have to hide under your desk. A nap is a brief sleep. Good night.
When you take a nap, you rest, usually during the daytime. In some cultures, everybody naps after lunch, while in other places naps are only for young children and elderly people. Sigh. A second meaning of nap is "slightly fuzzy texture," like the nap of a jacket or the nap of a rug. This kind of nap stems from the Middle Low German noppe, "tuft of wool."