Look up well drink in Wiktionary, the free dictionary.
A well drink or rail drink is an alcoholic beverage served using the lower-cost liquors stored within easy reach of the bartender in the counter 'speed rail' or well. Rail drinks differ from "call" drinks in that the former is offered when a customer does not specify a particular brand of liquor when ordering a mixed drink. The terms "well drink" and "rail drink" come from the name for a bartender's workspace, known as either the well or the rail. In any given establishment, the rail/well liquors available may be known as the "house pours" or "house brands".
A rail or well drink is usually served when a customer does not specify that a particular brand of liquor be used. For example, a customer order for a "Scotch and soda" would lead the bartender to use a rail/well Scotch whisky and would be priced as a rail drink, whereas ordering "Glenfiddich and soda" would be a call drink.
Call liquors are known as such because the customer "calls" or requests a particular brand of liquor.
Certain expensive brand-name liquors are not considered or priced as call, but are instead known as "top-shelf" liquors, both from their placement on the shelves and from their price relative to the other liquors available.
^ abcdefgLai, Anne, ed. (2005). Bartending 101: The Basics of Mixology. Harvard Student Agencies, Inc. (4th ed.). St. Martin's Press. pp. 7–9. ISBN9780312349066. In professional bars, a "speed rail" usually replaces the front bar. This rack, attached to the bar or sink directly in front of the bartender, holds "house brands" (usually less-expensive brands) of front-bar liquor. The bartender defers to the well brand of liquor for every drink unless the customer specifies a well-known brand, or "call brand," as it is known in bartending lingo. The more expensives call brands stay on the back bar. That means that you will prepare a White Russian with generic coffee brandy instead of the more commonly known call brand (Kahlua) unless the drink specifically requests otherwise (or if your bar is using Kahlua as its well brand). There is a further classification of alcohols called the "premium" or "top-shelf" brands. These are even higher quality bottles of liquor - such as Bombay gin or Old Grand Dad bourbon.
^ abcMeyer, Arthur; Vann, Mick (2013). How to Open and Operate a Restaurant (electronic ed.). Globe Pequot. p. 100. ISBN9781493001446. 'Well liquor' is the group of spirits that are used to make drinks when the brand is not specified by the guest ("scotch and soda"). 'Call' liquors are specifically requested brands ("Glenfiddich and soda").
^ abcFeinstein, Andrew H.; Stefanelli, John M. (2008). Purchasing: Selection and Procurement for the Hospitality Industry. John Wiley & Sons, Inc. p. 567. ISBN9780470314852. Well liquor, sometimes called the "house brand," is served when a patron asks for a shot of Scotch without specifying a particular brand. The term well derives its name from where this type of liquor is located, typically being stored in a well located just below the bar top. [...]Many foodservice and bar operations serve premium brands as their well brands. This is sometimes referred to as the "premium well"...
^ abKatsigris, Costas; Thomas, Chris (2006). The Bar and Beverage Book (4th ed.). John Wiley & Sons, Inc. p. 179. ISBN9780470073445. In short, the well is an important profit center that should reflect the bar's image and respond to the desires of its clientele.[...] To determine whether or not to upgrade your house pours to premium pours, ask yourself these questions: [...] Are the current house pours a liability? It's a fact that most bar owners stock their well and don't think much about it after that.
^Brown, Douglas Robert (2004). The Encyclopedia of Restaurant Forms1. Atlantic Publishing Company. p. C3-3. ISBN9780910627290. Call Liquor. Any liquor other than well liquor. The term refers to "calling" the liquor brand by name, such as "Captain Morgan and coke" rather than "rum and coke."