From the command go help packages
:
An import path is a pattern if it includes one or more “…” wildcards,
each of which can match any string, including the empty string and
strings containing slashes. Such a pattern expands to all package
directories found in the GOPATH trees with names matching the
patterns. As a special case, x/… matches x as well as x’s subdirectories.
For example, net/… expands to net and packages in its subdirectories.