1) A popular girl's name.
2) A slang term to refer to LSD (
lysergic acid diethylamide). The term "Lucy" comes from the song by the Beatles "Lucy
in the Sky with Diamonds" which is commonly thought to be about LSD.
Lucy is often used as a code word for LSD when referring to the drug in a public setting or over the phone where one does not want to openly discuss illegal
activities.
Lucy is used like a person's name in such discussions. Like saying "Lucy took me on a trip last night" to indicate you tripped on LSD the previous night.