A flip is a class of mixed drinks. According to the Oxford English Dictionary, the term was first used in 1695 to describe a mixture of beer, rum, and sugar, heated with a red-hot iron ("Thus we live at sea; eat biscuit, and drink flip"). The iron caused the drink to froth, and this frothing (or "flipping") engendered the name. Over time, the proportion of eggs and sugar increased, the beer was eliminated, and the drink ceased to be served hot.
The first bar guide to feature a flip (and to add eggs to the list of ingredients) was Jerry Thomas's 1862 How to Mix Drinks; or, The Bon-Vivant's Companion. In this work, Thomas declares that, "The essential in flips of all sorts is to produce the smoothness by repeated pouring back and forward between two vessels and beating up the eggs well in the first instance the sweetening and spices according to taste."
With time, the distinction between egg nog (a spirit, egg, cream, sugar, and spice) and a flip (a spirit, egg, sugar, spice, but no cream) was gradually codified in America's bar guides. In recent decades, bar guides have begun to indicate the presence of cream in a flip as optional.
Flip recipes from Jerry Thomas (1887) 
The following flip recipes appear in Jerry Thomas 1887.
- Cold Brandy Flip – brandy, water, egg, sugar, grated nutmeg
- Cold Rum Flip – substitute Jamaica rum
- Cold Gin Flip – substitute Holland gin
- Cold Whiskey Flip – substitute Bourbon or rye whiskey
- Port Wine Flip – substitute port wine
- Sherry Wine Flip – substitute sherry
- Hot Brandy Flip – brandy, sugar, egg yolk, hot water, grated nutmeg
- Hot Rum Flip – substitute Jamaica rum
- Hot Whiskey Flip – substitute whiskey
- Hot Gin Flip – substitute Holland gin
- Hot English Rum Flip – ale, aged rum, raw eggs, sugar, grated nutmeg or ginger
- Hot English Ale Flip – same as Rum Flip, without rum and less egg white
- Sleeper – aged rum, sugar, egg, water, cloves, coriander, lemon
- Jerry Thomas, How to Mix Drinks (New York: Dick and Fitzgerald, 1862), 60.
- Jerry Thomas' Bartender's Guide (1887) Cold Flip recipes on The Art of Drink
- Jerry Thomas' Bartender's Guide (1887) Hot Flip recipes on The Art of Drink