Butter flavored with herbs, garlic, wine or other seasonings, most often made by mixing them into softened butter. The butter is then rolled into a log shape and refrigerated until needed; slices are cut from the roll and placed directly on hot meat, fish or vegetable where it melts immediately, creating a sauce. Herb butter and anchovy butter can be forms of compound butter: it is the creation of the log and the slice-as-needed to create a sauce that creates the reference.
The French view this as a sauce. It is simply a flavored butter most often made by mixing liquid and/or solid ingredients into softened butter. This butter is then rolled into a log shape and refrigerated until needed. To serve, cut slices from the roll and place directly on a hot Piece of meat, fish, or vegetable. Serve immediately; the melting compound butter will make a sauce.