This is an excellent and very important question, as the rules can be confusing and mistakes can be costly.
The short answer is: It depends entirely on the country, the length of your layover, and whether you leave the airport’s international transit area.
Here’s a detailed breakdown:
Most countries distinguish between: Airport Transit: You remain in the international transit area of the airport and do not pass through immigration (border control). You are not legally “entering” the country. Entry: You pass through immigration, collect your baggage, and enter the country, even if just for a few hours.
If you stay in the transit area, you typically do not need a visa for that country. Your visit is not considered “visiting” for immigration purposes.
If you leave the transit area (to explore the city, meet someone, or even because your airline requires you to collect and re-check bags), you are entering the country and will need the appropriate visa or entry permit.