Alright kiddo, so when someone talks about hemline, they are talking about the bottom edge of a piece of clothing that has been cut to a certain length. Do you know what I mean by length? It's how long something is from top to bottom.
For example, a skirt can have a hemline that goes all the way down to your ankles, or it can have a hemline that only comes down to your knees. The length of the hemline can change the way the skirt looks and feels when you wear it.
Some people like to wear short hemlines because they think it makes them look cute or youthful, while others prefer a longer hemline because it can make them feel more formal or sophisticated.
Does that help you understand hemlines a little better, kiddo?