Dude is an American English slang term for an individual. It typically applies to males, although the word can encompass all genders. Dude is an old term, recognized by multiple generations although potentially with slightly different meanings.
From the 1870s to the 1960s, dude primarily meant a person who dressed in an extremely fashion-forward manner or a citified person who was visiting a rural location but stuck out. In the 1960s, dude evolved to mean companion, a meaning that slipped into mainstream American slang in the 1970s. Current slang retains at least some use of all three of these common meanings.