A cross-dressing ball is a party where people wear clothes that are typically worn by the opposite gender. This means boys might wear dresses and girls might wear suits or pants. It's like if you and your friends played dress-up together, but everyone pretended to be the opposite gender.
Some people like to cross-dress because they enjoy the feeling of wearing different clothes or want to express a part of themselves that they don't normally get to show. They might also feel more comfortable and confident in clothes that are typically worn by the opposite gender.
A cross-dressing ball is a special kind of party where everyone is encouraged to dress up in this way. It can be a lot of fun to see all of the creative outfits and to pretend to be someone else for a little while. It's important to remember that everyone should be respectful of each other's choices and not make fun of anyone for the way they look.