The Importance of Compassion

Sometimes I get stuck in my head thinking, is that even compassion? How do you know that's compassion? So I'm just curious if there is a definition of the feeling or a visual way to. In Tonglen, what I do understand is the description of poison. Thick, sludgy, smoky, dark, hot. Okay, but compassion, if you had to describe it, what does it feel like? We breathe that in to the doorway of our hearts and our hearts are connected to that whole great ocean of being; that's where we feel the compassion.