What is the meaning of dude?

"Dude" is a slang term for a man, first used by cowboys. "Dudette" is sometimes used as a slang term for a woman in surfer slang.

Dudes were originally the same as fops - men who dressed in the latest fashion without regard for practical clothing. Cowboys meant this term as an insult - surfers changed the meaning around and began using it as a friendly term for any male.