Classicism is like when someone wants to make something look really fancy, they try to copy the designs and styles from a really long time ago. You know how sometimes you see pictures of kings and queens with really fancy dresses and big wigs? That's what classicism tries to copy.
It's kind of like when you play dress up and put on a big, fancy dress that you got from your grandma's closet. You're pretending to look like a princess from a long time ago. People who liked classicism did that too, but with art, buildings, and even music.
They thought that the old designs and styles from places like Ancient Greece and Rome were the most beautiful and perfect. So, they made new things like buildings and paintings that looked like they were from a long time ago.
Some people really liked classicism because they thought it made everything look really important and powerful. But other people thought it was kind of weird to keep copying old styles instead of trying new things.
So, that's what classicism is: people trying to make things look really fancy by copying old designs and styles that they thought were the most beautiful.