Crypto-Judaism is the act of keeping Jewish beliefs, customs and practices a secret. It's like when you have something you really like, but you can't tell anyone else about it because they might not like it or it might not be safe to do so. This is what many people did during a time in history when being Jewish was not allowed in certain places.
Long ago, there were some places where Jewish people were not allowed to practice their religion. These places made it illegal to believe in Judaism and follow Jewish customs. So, instead of giving up their beliefs and traditions, some Jewish people chose to practice their religion secretly. This was called Crypto-Judaism.
To practice their religion without being found out, they would do things differently than other people. For example, they would not eat certain foods, such as pork, which is not allowed in Judaism. They would also have secret meetings to practice their beliefs and read Jewish texts.
Crypto-Judaism was dangerous for those who followed it, because if they were caught, they could be punished or even killed. So, they had to be very careful and keep their beliefs and practices hidden from others.
Nowadays, people are free to practice their religion openly and without fear of punishment. However, some people still choose to practice their beliefs in secret for various reasons, such as safety or personal preference.