Final answer:
A greyhound is a cocktail made from grapefruit juice and vodka, known for its tangy flavor and easy preparation.
Step-by-step explanation:
A greyhound is indeed a type of cocktail. Specifically, it is a cocktail with grapefruit juice and vodka. This simple but refreshing drink consists of these two ingredients, typically mixed in a highball glass over ice. Its popularity is due in part to its tangy flavor profile and the ease of preparation. If you were to rim the glass with salt, you'd have a variation of the greyhound known as a Salty Dog. The simplicity of a greyhound cocktail makes it a favorite choice for many cocktail enthusiasts.