In the world of distilled spirits, there is a lot of confusion about whiskey and the different styles of whiskies. Whiskey is a broad term much like the word beer. While beer may have a number of styles like pilseners, India pale ales and hefeweizens, whiskey encompasses range of styles from Bourbon to rye to Canadian to Irish to Scotch and more.
Essentially, whiskey is merely beer that has been distilled. No hops are used when making a distillers beer, but other than that, the initial steps are very similar prior to distillation.
So what is the definition of whiskey? Whiskey is a distilled spirit obtained from the fermented mash of grain, distilled at less than 190 proof, stored in oak containers and bottled at a minimum of 40% abv.
While gin and vodka are also generally distilled from a mash of grain, whiskey is unique in that it is the maturation process in oak that sets it apart. Maturation in oak makes a difference, more so with bourbon than, say, Irish whiskey, but oak is air permeable which helps oxidize the distillate and also releases flavor compounds through wood chemicals like lignin and vanillin. Additionally, by generally distilling at a lower alcohol by volume initially, more flavor compounds known as congeners remain in the distillate.By bottling at at least 40% alcohol by volume, the flavor of whiskey is not compromised and retains a richer, fuller flavor.
Remember that the word whiskey is an umbrella term, categories like single malt Scotch or Bourbon have much stricter rules and regulations. Just as beer has a wide variety of styles, whisky has a number of styles that all fall within this broad description.