Amaro simply means bitter, and the various slightly bitter herbal liqueurs known as amari are very popular in Italy as a digestivo to help the pasta go down.
Famous brands—each has a different recipe, with perhaps a score of different ingredients (herbs, roots, bark)—include Fernet-Branca, Ramazzotti, Averna, Amaro Lucana, Sibila, Borsci, Biancosarti and Cynar, made from artichokes. Foreign brands are also popular, such as Jägermeister and Unicum.
Each region has its own concoction, many of which are very much an acquired taste (where we used to live in Umbria, it was a poison known as Vipero, which had all the charms of a flat, warm rum and Coke).
Images by: Shabbychef, Creative Commons License