So everyone else is focusing on the memory allocation side of ownership. The other side to this is aliasing / borrowing / handling references and mutability.

So everyone else is focusing on the memory allocation side of ownership. The other side to this is aliasing / borrowing / handling references and mutability. In Python, you might have a `list` that you built up and them pass its data to multiple functions. You assume these functions are do not mutate their arguments and you keep passing the same `list` over again. In this case, the caller is controlling the invariants of the `list` and therefore "Owns" it. Deep down, one of those functions needs to mutate a `list` to do its calculations. Where the mutation is happening, it assumes it is the "Owner" and can modify the `list` without violating any invariants. Unfortunately, a "Borrowed" list was passed in and now the caller's invariants are violated. Rust's ownership model helps to catch this kind of problem at compile time. By default, everything is single-owner though you can change that with a `Mutex`.