What is a friend?

What is a friend?  This question has been running over and over thru my head all day long.  What characteristics does a friend have?  Is it someone you have a good time with or that you enjoy being around?  Or does it go deeper than that?  Is a true friend someone you trust will always have your back, or someone you believe will always be honest with you?  I'm anxious to hear any type of feedback about what friendship means to any of you.  I know what it means to me...and I count myself a lucky girl to have such a stellar support system.  My daughter, my lil sister, my mom, my other half...they are all amazing and the best friends I've ever known.  I am also blessed to have a core group of people who aren't blood but are amazing in their own way.  So what does being a good friend or having a good friend mean to you?