Rust: What is the difference between Waker and RawWaker?

1use std::task::{Waker, RawWaker, RawWakerVTable};
2
3// Safe Waker
4fn wake(waker: &Waker) {
5    waker.wake_by_ref();
6}
7
8// Unsafe RawWaker
9unsafe fn raw_waker() -> RawWaker {
10    RawWaker::new(std::ptr::null(), &VTABLE)
11}