What else would it stand for?

Having one program (process) talk to another is dangerous. Think of a stranger trying to come over to me and deliver a message. There's no way I can guarantee that he isn't planning to stab me as soon as he sees me.

That's why we have special mechanisms for programs talking to other programs. Instead of having the stranger deliver the message directly to me, our mutual friend Bob (IPC Library, binder in this case) acts as an intermediary. This way at least I can't be "directly" stabbed.

What's preventing the stranger from convincing Bob to stab me? Not much (except for Bob's own ethics/programming)

To work around this, we have designed programming languages (rust) that don't work if there's a possibility of it being corrupted (I would add "at least superficially", but that's not the main topic here). Bob was trained by the CIA in anti-brainwashing techniques. It's really hard to convince Bob to stab me. That's why it's such a big deal. We now have a way of delivering messages between two programs that is much safer than before.

The only problem is that the CIA anti-brainwashing techniques (rust) tend to make people slow. So we deliver messages less efficiently than before. Good news is in this case we managed to make Bob almost as fast as before, so we don't lose our own much while gaining additional security. The people who checked on Bob even made sure to have Bob do the exact same thing as before when delivering messages (using RB Trees), hence this evidence is most likely credible.

Distros will work a bit at shipping the right toolchain the first time they ship a rust-written module, but otherwise, it can't break userspace. I guess they'll start by merging the close reimplementation to make regressions easy to track.

The C binder driver has been in the mainline kernel for one or two years at this point.