While there are many words that are interchangeable — like whiskey and water — but liquor and liqueur are not. While the first four letters of the words are the same, and they both can be found in a cocktail, that is where the similarities end. And asking for one, when you mean the other, at a bar can result in a very disappointing drink.
Liquor is essentially any "unsweetened distilled alcoholic beverage," Serious Eats noted. This means popular booze like vodka, tequila, whiskey, pisco and rum all qualify. It's not uncommon for people to treat liquor and spirit as synonyms, said Vinepair. Some, however, consider spirits to be "any distilled alcohol" including methanol and butanol, while liquor is the drinkable stuff. "This is hair-splitting," Serious Eats said, and most people don't make that differentiation.
Liqueur on the other hand means a "sweetened distilled alcoholic beverage" and is made from liquor. It generally has a lower proof, too. Typically, liqueur in France contains "at least 100 grams of sugar per liter," Andrew Willett noted in Elemental Mixology. In the United States, a liqueur is "any liquor that is sweetened to the point of containing at least 2.5% sugar syrup, by weight, in the finished product." Popular liqueurs include triple sec, absinthe, Aperol, triple sec, cinnamon schnapps and Kahlua.
Stateside, the term "cordial" is often used in place of liqueur. Though, as Serious Eats noted, cordial "tends to appear more often on dessert-like products" such as chocolate and coffee-flavored liqueurs. In the U.K., cordial can also mean any "very sweet nonalcoholic beverage." So definitely know where you are ordering a drink.
So where do flavored spirits like the err, modern, creation that is whipped cream vodka fall? It all depends on just how much sugar is being used in the drink. If there is a hefty amount of sweetener used and it meets the aforementioned definitions then it can qualify as a liqueur. A representative for the popular vodka brand Absolut noted on a forum, however, that there is no sugar added to the flavored versions of its vodka, making it a spirit.
If this is all too much for you, feel free to stick to wine, which falls into neither category and can be very, very affordable.