A true friend is your support system. They're always there for you no matter what you're going through in life. However busy they may be, they always take some time out for you. They accept you for who you are inside, not what you seem to be on the outside.
They always lend you a patient ear, and listen to all your problems, however big or small. You feel free to share your insecurities with them, and can be sure that they won't use it to exploit you.
You can be yourself with them. You're never scared of telling them anything. You know that all your secrets are safe with them, and that they won't judge you.
Also, they help you to find the right path if you're ever lost. They warn you if you are going in the wrong direction.
They just want you to be happy, without any ulterior motive.