Short definition
The very first impression a wine makes when it hits your palate, before you have time to analyze it.
The attack is that split-second first impression — is the wine bright? Rich? Aggressive? Subtle? Professional tasters evaluate attack separately from mid-palate and finish because a wine can start bold and fade, or start quietly and build. Champagne often has a striking attack from its acidity and bubbles. A soft Merlot has a gentle one.