Pathos is a quality that stirs emotions. A song with a lot of pathos hits you right in the heart.
You ever notice how some songs or movies appeal to your brains, while others appeal to your feelings? The ones that are all about feeling are full of pathos, an appeal to emotions that originally meant "suffering" in Greek. Often, this word has to do specifically with pity and sympathy: when someone tells a story about people suffering that makes you feel for them, that's pathos.