Gin is the spirit mixed with lemon juice, sugar and carbonated water in a classic Tom Collins cocktail.
The traditional drink combines gin, fresh lemon juice, sugar syrup and soda water. It is shaken or otherwise mixed before being served over ice in a tall Collins glass, usually with a lemon slice or cherry garnish.
The name “Tom Collins” also refers to the older John Collins family of drinks. John Collins was associated with a gin-based mixture, while the Tom Collins name became standard as Old Tom gin was used in some nineteenth-century versions. Old Tom gin is a lightly sweetened style that is historically important to the drink’s name.
Recipes have changed over time, and a “Collins” can now be made with other spirits, such as whiskey or vodka. Those are named specifically, such as a John Collins or vodka Collins. Without another qualifier, the classic Tom Collins is the gin version.