A lucid dream.
"During her vivid sleep, she had a truly lucid dream where she realized she was flying and decided to explore the entire city before waking up."
(of language) transparently clear; easily understandable
"writes in a limpid style"
"lucid directions"
"a luculent oration"
"pellucid prose"
"a crystal clear explanation"
"a perspicuous argument"
transmitting light; able to be seen through with clarity
"the cold crystalline water of melted snow"
"crystal clear skies"
"could see the sand on the bottom of the limpid pool"
"lucid air"
"a pellucid brook"
"transparent crystal"
clear; easily understood
"Her lucid explanation of the complex contract terms finally helped me understand what I was signing."
A surname, from Irish​.
"The Lucid family has lived on this farm for three generations."