Russian reversal is a type of joke that flips the meaning of a phrase or statement in a funny way. It's called "Russian" reversal because it's similar to something called a "Yiddish" or "Borscht Belt" joke, which was popular in Jewish comedy clubs in the 1930s and 40s.
Here's an example of a Russian reversal joke: "In America, you wear a T-shirt. In Soviet Russia, T-shirt wear YOU!"
This joke is funny because it takes a familiar phrase ("wearing a T-shirt") and flips it around to mean the opposite. The joke is also a little silly because it imagines a world where T-shirts are in charge instead of people. This type of humor can be a little confusing for young children, but as you get older and learn more about language and culture, Russian reversal jokes can be a fun way to play with words and ideas.