In Rust 2018 the "crate namespace" now lives outside of the "crate root", yet the reference and the compiler still refer to it as the "crate root". So if you write ::foo::bar this looks up foo in the "crate namespace", but the compiler still calls this the "crate root" as can be seen here:

error[E0412]: cannot find type `Bar` in the crate root
 --> src/lib.rs:4:16
  |
4 |     fn ok(_: ::Bar) {}
  |                ^^^ not found in the crate root
  |
help: consider importing this struct
  |
4 |     use crate::Bar;
  |

The help even implies that Bar is indeed in the "crate root".

The reference seems to have a similar problem: https://doc.rust-lang.org/reference/paths.html#path-qualifiers

Paths starting with :: are considered to be global paths where the segments of the path start being resolved from the crate root.

I'm not sure if a proper term for the crate namespace got defined, but it's ambiguous at the moment and causes confusion for beginners: https://twitter.com/mcclure111/status/1368658525891747845