Amer Picon is a bitter cordial made with orange, gentian, and other ingredients. It has a bold bitter flavor and is often used as a digestive. At the current time, this product can be fairly difficult to find, and in fact doesn’t appear to be available in the US at all.
A substitute product was recently brought onto the market by the “Torani” company (best known for the coffee syrups that they make for espresso stands), called simply “Torani brand Amer”. Unfortunately, while a good product on its own, it is not a suiteable replacement for Amer Picon in recipes that call for it.