Definitions for "Lucid dream"
A dream in which the dreamer becomes aware that they are dreaming, and can carry on the dream with unbroken awareness.  Dreaming in this state is a skill which can be learned.  Lucid dreams, like all dreams, usually occur during REM sleep.  Most of us have had a lucid dream during our life, whether we remember it from childhood (a high-level lucid dream) or from two days ago (a low-level lucid dream).
A dream in which you know you are dreaming.
a dream in which it occurs to the sleeping mind, "This is a dream