off of wikipedia
A lucid dream is a dream in which the person is fully aware that they are dreaming while the dream is in progress. In a lucid dream, it is often possible to exert conscious control over the dream characters and environment, as well as to perform otherwise physically impossible feats.
A lucid dream can begin in one of two ways. A dream-initiated lucid dream (DILD)[1] starts as a normal dream, and the dreamer eventually logically concludes that they are dreaming. A wake-initiated lucid dream (WILD),[2] which is sometimes considered more difficult to achieve, occurs when the dreamer goes from a normal waking state directly into a dream state with no lapse in consciousness.
Lucid dreaming has been researched scientifically, and its existence is well established.[3][4] Researchers such as Allan Hobson with his neurophysiological approach to dreaming have helped to push the understanding of lucid dreaming into a less speculative realm.