The term Portuguese refers to the people and culture originating from the Western European region of Earth.
During a discussion between Deanna Troi and Samuel Clemens in 2369, Clemens' who assumed that the nature of the USS Enterprise-D was one of "military conquest," rather than "exploration", mused that the same was said by all conquerors, including the early Spanish, Dutch, and Portuguese explorers, who revered themselves as also being "explorers". (TNG: "Time's Arrow, Part II")
When the Leonardo da Vinci hologram was stolen from the USS Voyager and brought to an alien planet, Captain Janeway tried to explain the rescue attempts of the Voyager to him by claiming that there were Portuguese sailors trying to rescue them and that they were now in the "New World". (VOY: "Concerning Flight")