A lucid dream is a dream in which the dreamer takes complete control of all the events in their dream. They can do anything that they want as long as they stay in control, even waking up whenever they want.
Tom Paris described a past experience in which he was able to fly. Chakotay used a lucid dream to make contact with a group of unnamed aliens that were taking over the crew of USS Voyager in their dreams, choosing the image of Earth's Moon to "remind" him that he was dreaming. (VOY: "Waking Moments")