LSD, slangily is an acronym for lysergic ACID diethylamide, a powerful hallucinogenic drug. It is commonly referred to as 'ACID' and is often used recreationally. LSD has been used in various forms since the 1950s and is known for its ability to produce intense visual and auditory hallucinations. It is also associated with altered states of consciousness and can cause changes in perception, thought, and emotion.