So, back when the Soviet Union existed, people who wanted to travel outside of the country needed a special paper called a passport. Think of it like a permission slip to leave the country. Every Soviet citizen could get a passport, but it wasn't always easy because the government decided who could get one and who couldn't.
If someone did get a passport, they had to be really careful not to lose it because it was very important. It had their name, picture, and other important information on it, like where they were allowed to travel and how long they were allowed to stay.
People also needed visas to travel to other countries, which were like special permission slips to enter a specific country. So, if someone wanted to go to a place like the United States, they needed both a passport and a visa.
The Soviet government used the passport system as a way to control where people went and what they did. They didn't want people to leave the country and learn about life outside the Soviet Union, because they thought that would make people unhappy with the way things were in their own country.
So, the passport system was both a way for people to leave the Soviet Union and a way for the government to control where they went and what they did.