The document defines a liqueur as a sweetened and flavored spirituous liquor. Liqueurs typically contain 30-65% alcohol and have three main elements - a spirit base like brandy or rum, flavoring agents, and a sweetener. While originally developed as medicines, liqueurs are now commonly used in cocktails and cooking. Some important liqueurs mentioned include Advocaat, Benedictine, Calvados, Cointreau, Creme de Cacao, Izarra, Kahlua, Tia Maria, Slivovitz, and Malibu.