What is the term for people who travel across borders of different countries?

The term that best describes people who travel across borders of different countries is "tourists." Tourists are individuals who journey to a foreign country for leisure, business, or other purposes without the intent of settling there permanently. They often seek to explore new cultures, visit landmarks, and engage in recreational activities.

On the other hand, while emigrants leave their home country to live in another, and immigrants settle in a new country after moving from their original nation, these terms don't specifically capture the notion of travel in a temporary sense. Refugees, meanwhile, are people forced to flee their home country due to persecution, war, or violence, and their situation implies a more permanent relocation rather than travel for leisure or temporary purposes.

Hence, "tourists" specifically highlights the aspect of crossing borders for transient experiences, making it the most appropriate choice.