What does "wear her heart on her sleeve" mean?

Vocabulary Word: wear her heart on her sleeve

1. Definition (expr.) express deep feelings, show emotions, show passion, display the things one is feeling inside

Examples “Jeff is a really emotional guy. He always wears his heart on his sleeve. It’s fun to be around him because he’s always honest.”

Examples “My dad is a really guarded person. He never shows how he feels. No matter if he’s really happy or really sad, he always acts the same way. Sometimes I wish he would wear his heart on his sleeve so I could tell what he was thinking and feeling.

Examples “My little brother always wears his heart on his sleeve when he’s playing sports. He gets really emotional. You can see his intensity on his face.”

Examples “Sometimes I wish my girlfriend didn’t wear her heart on her sleeve all the time. I get tired of dealing with all of the emotion. It would be great if she would just be calm and normal once in a while. Instead, she’s always got something going on that we have to talk about – and usually she’s crying when we’re talking.”