Traits or Roles as they are called in Perl6 are described in detail in Apocalypse 12. On CPAN there are Class::Roles and Class::Role which aim to bring the Role functionality to Perl5.
Traits (as described in the papers and implemented in Class::Trait) are not the same thing as Roles (as defined in the Apocalypse) anymore. It is my understanding that the original Traits paper was the inspiration for Roles, but they have really grown to differ in many ways, and really should not be thought of as the same thing anymore.