A salty dog is a cocktail of gin, or vodka, and grapefruit juice, served in a highball glass with a salted rim.

The salt is the only difference between a salty dog and a greyhound.

Historically a gin drink, it is believed to date back to the 1920s.

[1] The drink is 2 fluid ounces of gin, or vodka, mixed with fresh grapefruit juice, shaken, and poured into a glass whose rim has been salted.

[2] The salty dog is a favorite drink of Artie (the producer played by Rip Torn) on the sitcom The Larry Sanders Show.