Compassion is the act of recognizing that the pain we feel as humans is universal, that it binds us all together despite whatever overt differences seem to be too difficult to surpass, and taking action to help alleviate that pain for others.
It is an intellectual and emotional act.
It is also physical, you can feel it rush through you when your heart grants access to its deepest depths which hold that limitless source of love, and it floods through you, invigorating your body and mind, inspiring you to act.