How is a liqueur typically defined?

A liqueur is typically defined as a flavored spirit that has been sweetened. This definition highlights the two key characteristics of liqueurs: flavoring and sweetness. Liqueurs are produced by infusing neutral spirits with various ingredients such as fruits, herbs, spices, or other flavorings, followed by the addition of sugar or other sweetening agents. This process not only enhances the flavor profile but also gives liqueurs their characteristic sweetness, setting them apart from other spirits.

In contrast, the other options refer to entirely different categories of beverages. A spirit distilled from grains generally pertains to spirits like vodka or gin but does not include the flavoring and sweetening aspects associated with liqueurs. A pure fruit fermented beverage, such as fruit wine, is not distilled and lacks the same process that characterizes liqueurs. Aging a spirit in oak barrels refers to the maturation process of certain spirits, like whiskey or rum, and does not inherently involve the flavoring or sweetening processes of liqueurs. Thus, the defining aspects of a liqueur are specifically centered on its combination of flavor infusion and sweetness, making "a flavored spirit that has been sweetened" the accurate definition.