Not to be confused with utsudere.
While a full smile on shundere character's face might be out of the question, their love interest can help them open up and feel accepted. They have a tendency to ignore and avoid other people. Shunderes are sad all of the time.
The second type of Shundere is that they don’t show their sadness to people and hide it all the time but they are actually really sad constantly. If they really are seen smiling, it might probably be a false smile that they show in public to hide their true inner sadness.
Meaning of the Name
The word is a compound of "shun..." (しゅん。。。), a Japanese sound effect representing melancholy, down, sad, depressed, etc., and "deredere" (デレデレ), which means "lovey dovey".