Bunnies have been a staple of the Playboy brand since it opened its first nightclub in 1960.
In the beginning, the bunnies were simply young women who worked as waitstaff in Playboy's clubs.
From 1960 to 1986, the brand ran 40 nightclubs, according to Atlas Obscura, as well as some intermittent casinos in England and the Bahamas. Prospective bunnies had to audition in order to get the job.
Since then, the term has expanded somewhat. It's even been applied to Hugh Hefner's girlfriends, who lived with him in the Playboy Mansion. Hefner ex-girlfriend Holly Madison's tell-all book is called "Down the Rabbit Hole: Curious Adventures and Cautionary Tales of a Former Playboy Bunny." Make no mistake, though — models who appear in Playboy magazine itself are "playmates," not bunnies.