Short definition
Flavors of vanilla, toast, caramel, or spice imparted to wine by aging in oak barrels.
Oak barrels give wine vanilla, coconut, baking spice, and smoky notes. New barrels add more flavor than used ones. American oak leans toward coconut and dill; French oak gives more subtle vanilla and spice. Too much oak can bury the fruit underneath — like drowning a good steak in sauce. Stainless steel-aged wines have zero oak influence.