Giffard Poire William (William Pear) liqueur is one of their classic liqueur expressions. It is a pear eua-de-vie sweetened to balance the pear.
Giffard is a French company specializing in a wide variety of liqueurs and eua-de-vie among other products. Some of those extra products are flavored cocktail syrups (or "sirop"). They are generally sweetened with pure cane sugar.