This is butter from which all milk solids has been removed. The result is a clear yellow fat that can be heated to a higher temperature than butter before burning.
It is an excellent fat for pan-frying.
Put the butter in a heavy saucepan over low heat. Melt gently. Skim off all the froth from the surface. You will then see a clear yellow layer on top of a milky layer.
Carefully pour the clear fat into a bowl or jug, leaving the milky residue in the pan. Discard the milky residue or add it to soups.
Since clarification removes impurities, clarified butter keeps well - several weeks in the fridge and longer in the freezer.
As a dip for seafood such as lobster and crab and for globe artichokes.