The term Latin refers primarily to the people and culture who lived primarily on Earth in the regions of Mexico on throughout South America. It was closely related to the Spanish.
During his initial analysis of the passengers discovered aboard the SS Botany Bay, Montgomery Scott noted that the crew was comprised of several mixed types, including Western and Mid-Europeans, Latins, and Orientals. (TOS: "Space Seed")
Jean-Luc Picard and Geordi La Forge both enjoyed Latin music. (Star Trek: First Contact, TNG: "The Mind's Eye")
The draft proposal for Star Trek: The Original Series, Star Trek is..., contained a character called José Ortegas, who was said to conform to the stereotypical Latin temperament, but less so the stereotypes about Latin men as lovers.