In Mu§

See primary documentation in context for trait is export

multi trait_mod:<is>(Mu:U \type:$export!)

Marks a type as being exported, that is, available to external users.

my class SomeClass is export { }

A user of a module or class automatically gets all the symbols imported that are marked as is export.

See Exporting and Selective Importing Modules for more details.

In Routine§

See primary documentation in context for trait is export

multi trait_mod:<is>(Routine $r:$export!)

Marks a routine as exported to the rest of the world

module Foo {
    sub double($xis export {
        2 * $x
    }
}
 
import Foo;         # makes sub double available 
say double 21;      # 42 

From inside another file you'd say use Foo; to load a module and import the exported functions.

See Exporting and Selective Importing Modules for more details.