I’ve seen this gesture in movies and my friends use it sometimes. You use it when you say goodbye to someone and you kinda tap on the side of your forehead with two fingers. I’ve attached an image with Brad Pitt doing this in once upon a time in Hollywood. Does anyone know what this gesture is called? Where it comes from, and what it means? Thanks! 
Learn English – this goodbye hand gesture called
word-request
Related Solutions
Shadow play, hand shadows, or shadow puppets will all probably be understood, although when I hear "shadow puppets" I usually think of things like this:
An older name for shadows thrown by hand is simply hand shadows. I've got this book, originally published in 1859, facing me on my bookshelf right now:
You can see how the popularity of the terms has changed over time.
The word is net.
I'm a maths teacher, and this is the standard term used in Australia. I'm fairly sure it's the same in other parts of the English-speaking world, thanks to sources like:
It's worth noting that this is not a common thing for most people to talk about, and unfortunately, "net" also has other (more common) meanings. A descriptive phrase, like your "unfolded thing", would be useful to name it when talking to people unfamiliar with the correct name.
Best Answer
I’ve never actually heard a name for it. Broadly speaking, I would just call this a kind of salute, and, specifically, a two-finger salute. Wikipedia has an entry for this: