What even is a flat white

I was born at a very young age, so you have to forgive me, but my whole life I've only drank an iced coffee, and that might be because I'm from Massachusetts, but the other day I was in a coffee shop and this cool British guy was like, you know all the flat white, and everyone thought that was cool, and I wanted to be cool, so then I ordered one, never had one before, oh my god, rocket fuel, I'm having one right now, not even sure what it is, all I know is that I'm sweating, my heart is racing, I'm anxious, but god I'm having a good time doing it.