Vest/vest/ Definition 1 of 4Pro Tip 1/3Formal Attire Vests are often part of formal wear, combined with suits and ties. He donned his vest for the formal gala. Pro Tip 2/3Layering Piece A vest acts as a middle layer between a shirt and a suit jacket. She chose a silk vest to layer her business attire. Pro Tip 3/3Casual Options Informal vests, like vest tops, are worn for casual occasions. On a hot day, he opted for a lightweight vest top.