Why bracket? The reason is that there is not only ket vectors |v> but also functionals <u| that can be applied to them, which will look like this <u|v>. So there are brackets around the construct. Think <bra|ket> if you like.
Sometimes I don't know whether to be proud of or disappointed in our species.
Yeah, it's not like any programmers have ever come up with bizzare and useless names for abstractions.
Clearly OT but the excessive reliance on foo and bar in many of my early C lang learning examples really slowed down my ability to transfer said techniques into something meaningful. Eventually one of my friends working in the Visual C++ team (I'm dating myself here) explained the connection of foo and bar to fubar and kind of felt like this!
I had the same experience; that's mostly what I'm referencing. Trying to use things like The Hacker's Dictionary (largely in-jokes, bad jargon, and obnoxious circular definitions) to clear it up made the problem worse. I get that it's just a humor book, but still.