> Aren't 'a and 'b sets of memory a reference can refer to?
No, the set of memory the reference refers to is encoded by the reference's bits. Two references with the same lifetime can refer to different memory, and vice-versa. Lifetimes determine when the reference is valid.
Strictly speaking, a pointer points to 1 address, not a set.
Abstractly speaking, a lifetime represents a set of memory that lives a certain length of time, and thus also represents the set of memory a reference with that lifetime can reference.
It's just a different way of thinking about lifetimes which helped me understand them.
Rust "fat pointers" like `&str` contain a length as well.
> represents the set of memory a reference with that lifetime can reference.
No, you can have memory that is alive for a particular lifetime but that you are not allowed to access via a pointer with said lifetime (because it's out of bounds).
