No, it means that at runtime the representation of `Option<~T>` is simply a nullable pointer (this is also how borrowed pointers are represented at runtime, i.e. with no overhead whatsoever compared to C-style pointers). It's simply a perfectly-safe memory optimization (the language leaves the runtime representation of enums (of which Option is one) deliberately unspecified so that these types of optimizations can be made). It doesn't make Rust any less safe, as the language itself still has no notion of null pointers.