Wikipedia: In most societies throughout the world, siblings usually grow up together and spend a good deal of their childhood socializing with one another. This genetic and physical closeness may be marked by the development of strong emotional bond such as love or enmity.
Urban Dictionary: your sister is the girl that will always be there for you and may save you one day, whether you know it or not. your sister may or may not be related to you and could just be an amazing friend, but either way your sister is always slow to judge and quick to forgive. she will always love you, she might just hide it from you.
Unknown: A sister is someone who's been where you've been, who knows you and what you're about... Someone you know you can call if you need to when something's just not working out. A sister is someone who's more than just family her friendship is one of a kind... And the closeness you've shared through life's laughter and tears is the deepest that you'll ever find.
Today, the thing people lay awake at night and dream about happened to my sister. Her best friend moved away a few months ago... and today, she showed up completely unexpected at our door. The happiness that was radiating off Maya was tangible, she had this huge smile on her face, she even started to cry. I understood completely... I realized that this was something I'm sure she's been hoping, one of those wild "wish upon a star" hopes, that this would happen someday. Any day. It's something I do. I would have burst into tears if Ashley, Mik, or Chris had shown up at my door unexpectedly. They are all people I miss more than one can really imagine. It's an incredible joy, to have someone so close you, that they feel like sisters. To have a friend that you can confide so deeply in, that it doesn't matter what color you are, where you were born, the fact that you don't live together (sometimes that's a good thing). You're just the best of friends, that one can have.
It amazes me how much people affect other people. Like my boss said the other day, "no man is an island". We need people... but I think I just realized how much.