It expresses regret or disappointment about something.
Here are some examples:
* "Dommage que tu ne puisses pas venir." (Too bad you can't come.)
* "C'est dommage qu'il pleuve." (It's a shame that it's raining.)
* "Dommage que le film soit déjà terminé." (Too bad the movie is already over.)
Let me know if you have any other French words you'd like to understand!