Liqueurs are historical descendants of herbal medicines. They were made in Italy as early as the 13th century, often prepared by monks, for example, Chartreuse.
Nowadays, liqueurs are made worldwide in a huge range of styles and flavours. They’re also are served in many ways, for example, straight, over ice, with or in coffee, or mixed with cream or other mixers to create cocktails. They’re often served with or after a dessert, and used in cooking.