What is the idiom wear your heart on your sleeve mean?

The idiom "wear your heart on your sleeve" means to openly express your emotions and feelings, rather than keeping them hidden or guarded. It suggests a level of vulnerability and authenticity, as someone who wears their heart on their sleeve is willing to show their true feelings to others. This expression often implies that the person is honest and straightforward about their emotions, whether they are happy, sad, or in love.