Short definition
The framework of tannin, acidity, and alcohol that gives a wine its shape and aging potential.
Think of structure as a wine's architecture. A well-structured red has firm tannins and bright acidity that will let it age for years. A wine with poor structure feels flat or flabby, like a building without a frame. Bordeaux and Barolo are famous for structure; Beaujolais trades structure for easy-drinking charm.