Amer Picon, now known as simply Picon, is an orange bitters aperitif made in France. It comes in two styles: Picon Biere, intended for consumption with beer as a mixer or chaser; and Picon Club, intended for use with wine. It's the latter that is generally used in cocktails, but the former will suffice if the latter is unavailable.
One problem with this product is that it was reformulated in the 1970s, resulting in a product with a lower ABV and a somewhat different character than before. As a result, classic cocktails calling for this ingredient are very difficult to recreate as originally intended.
As Amer Picon is very difficult to find in the United States, since currently no US company imports or distributes it, Torani Amer is often used as a substitute.
Cocktails calling for Amer Picon include the Picon Punch.