What is Friendship?

As we went over in class different kinds of virtues and what they really are, I find myself questioning whether what I think friendship is. You always hear in movies, read in books, and hear people say what friendship is and how they make friends with another person or even how someone is not really your friend if they are doing something against you. For me, friendship is loyalty, truthfulness, to be there when he/she is needed, to listen, to be good, and various other qualities. But I wonder now is that truly friendship? A bad person can be loyal. They can be truthful in their own mind. They can listen and fit the other qualities. Maybe not all of them, but every person has their faults. No one is perfect. Can I say someone is being my friend when there's no universally applicable definition for it? What is friendship?