An international certificate of vaccination or prophylaxis is like a special piece of paper that shows you have gotten shots to protect you against certain diseases. It's kind of like how when you go to the doctor for a check-up and they give you a shot to help keep you from getting sick.
But this special paper isn't just important for your health - it's also important for traveling to other countries. Sometimes when you go to a different country, they might ask to see this paper to make sure you've gotten the right shots to keep you and the people who live there safe.
So, if you and your family are planning to travel to another country, you might need to go to the doctor beforehand and get some shots. Then the doctor will give you this special paper to show that you've been vaccinated against certain diseases. And when you go through customs in the other country, you might have to show this paper to prove that you're healthy and safe to be there.