Imagine you have a toy that you used to love playing with when you were younger. You remember all the fun you had and all the good times you shared with that toy. Even though you've grown up and you have new toys or hobbies, you still feel a warm and happy feeling when you think about that old toy. This feeling is called nostalgia, which means you miss something from the past.
Now, some grown-ups feel this way about a whole country called the Soviet Union. This was a big country that used to exist a long time ago, from 1922 to 1991. In the Soviet Union, people shared everything equally and everyone had a job and a place to live. Some people who remember those times feel happy and nostalgic about them because they remember they had stability back then. They didn't have to worry about money or food or healthcare because the government provided that for everyone. They also felt a sense of pride because the Soviet Union used to be very powerful and important in the world.
But not everyone feels this way. Some people remember the Soviet Union differently - they remember the lack of freedom or the poor quality of life or the oppression, which means they didn't have a lot of choice in how they lived or spoke or thought. They didn't have the same opportunities as other people and they felt trapped.
So nostalgia for the Soviet Union is like having a happy memory of the past, but it's something that grown-ups feel about a whole country that doesn't exist anymore. Some people loved the Soviet Union for the good things it did, while others didn't like it for the bad things it did.