Why are Some golang.org Packages Prefixed with an `x`

Question

Why are some golang.org package names prefixed with an x? The specific package that piqued my interest was bycrypt

My main concern is the x

Answer 1

The x means external. They are developed outside of the golang core. Experimental packages are under golang.org/x/exp

Refs: https://golang.org/pkg/#subrepo https://groups.google.com/forum/#!msg/golang-nuts/eD8dh3T9yyA/l5Ail-xfMiAJ

Answer 2

Packages that are prefixed with X are part of the go project but are stored in sub repos. They are not experimental.

See: https://golang.org/pkg/#subrepo