Most commonly, when we use the word oak, we mean to describe the flavor that new (or nearly new) barrels bestow upon wine that has spent time inside them. This flavor can vary, but usually anything that smells like coconut, vanilla, cedar, cloves, nutmeg, cinnamon, or, well, the split wood of oak trees, is a dead giveaway for aging in new (or newish) oak barrels. Uncertain? Go pour yourself a glass of bourbon, and smell that. There's what oh-so-much oak smells like. Whole splintery planks of it.