This is a type of glass for spirits, especially brandy. It’s designed to be wide at the bottom and narrow at the top, which gives the liquor a large surface area to evaporate and traps the vapors and the scent of the drink.
People “sniffing” a snifter of brandy is a common trope. Presumably, this is where the name came from – the glass is specifically designed for smelling.
Technically, the snifter should be allowed to lay on its side, and the correct amount of liquid is just enough that it won’t spill (see image). However, I mentioned this to a veteran bartender (at the same time I took the picture), and he had never heard this.
Why I Looked It Up
I tried to become a brandy drinker. It did not go well. But it did leave me wondering what a snifter was.