This generally means what they can produce and provide most efficiently, with the least amount of resources, at a lower cost than competing nations.
In a globalized economy, countries specialize in the products and services they have a competitive advantage in. This generally means what they can produce and provide most efficiently, with the least amount of resources, at a lower cost than competing nations. If all countries were specializing in what they do best, production should be more efficient worldwide, prices lower, economic growth widespread and all countries benefiting -- in theory.