So, a long time ago, there was a country called the Soviet Union. The government that ran the country didn't really like religion, which is when people believe in God or other higher powers.
The leaders of the Soviet Union wanted everyone to believe in the same ideas, so they didn't like it if people believed in different religions because those ideas might go against what they wanted.
They even made laws that said people couldn't go to church or practice religion freely. People who did were sometimes punished or put in jail.
That is why the Soviet Union was known as an "atheist" society, which means they didn't believe in God or religion. However, some people still wanted to believe in these things, so they did it secretly or only with close friends and family.
Eventually, the Soviet Union stopped being a country, and people were allowed to believe in whatever religion they wanted without fear of punishment.