Vests and waistcoats have some distinct differences, and men wear both garments. The most crucial difference between the west and the waistcoat is that a vest is a casual garment that can be worn without anything under it. A waistcoat is a formal jacket that is usually worn over a shirt.
A waistcoat is part of men's formal wear when worn with a necktie, and it is also the third piece of the standard male business three-piece suit. There are different types of vests for various purposes, but waistcoats generally only serve one purpose, as they are all relatively similar.