What Is The Tilde Key?

I'm following a video tutorial and I'm being asked to press the "tilde key". I don't really know which key is that.
I've looked for it in my keyboard, but I can't find it.
Can someone at least tell me how does the "tilde key" is supposed to look?
Is it possible that key is not in my keyboard?

This is the tilde key ~
You are supposed to have it in your keyboard, if it's missing then it's possible you have a weird foreign keyboard.
Where is it?
You can find it above the tab key and below the escape key.
Or to the right of the number 1 key.

That was meant to say, to the left of the '1' key, not the right.