Not only is this a brillaint song featuringJohn Lennon with his most wailing voice ever, but it is also slang for that ever popular drug of choice, LSD
a song written by the Beatles after John Lennon's son came home with a drawing of one of his friends named Lucy O'Conner, and John asked who it was he replied:
One of The Beatles famous songs. Many people think its song about LSD but, it's not. The song was inspired by John Lennon's son, Julian. He brought home a drawing of a girl in his class, named Lucy, and she was floating in the air and he drew stars around her. Julian named the drawing: Lucy in the Sky with Diamonds.
It has nothing to do with LSD, it's all a kids song.