I've only ever seen whipped butter for sale in plastic tubs at the supermarket. I'm pretty sure it's just whipped with air. It's an unusual/niche product; almost all butter is sold as solid sticks.
It's true that diners often provide whipped butter, probably because it melts easier than a solid "pad" of butter. It comes in little round plastic packets, similar in shape to coffee creamer packets.
The other reason it exists is to fool the consumer: to make them think they're getting more than they actually are. In the case of butter, this can be a good thing for health reasons. There's a kind of placebo effect where you think you've put a lot of butter on your pancakes but it's really not that much.
by Holly D
Click any of the links below to automatically search the given site for: How do you make whipped butter?