A sister is a girl or woman who shares one or both parents with you. If you and another person have the same mother and father, you're siblings, and if that sibling is female, she's your sister. Brothers and sisters grow up in the same family, which creates a unique bond that can last a lifetime.

Sisters often know each other in ways that friends can't, simply because they share so much daily life: the same house, the same parents, the same family traditions and inside jokes. They might fight over who gets to sit in the front seat or whose turn it is to do the dishes, but they also share secrets, protect each other at school, and remember all the same family stories.

The relationship between sisters takes many forms. Some sisters become best friends who talk every day. Others might clash constantly when they're young but grow closer as adults. Twin sisters experience many things at the same age. Older sisters might feel responsible for younger ones, while younger sisters sometimes feel they're living in their older sister's shadow.

People also use sister for close female friends (“she's like a sister to me”) or for women who share a common bond, like members of the same organization. Nuns call each other Sister, and women fighting for the same cause might call themselves sisters in that struggle.

The word captures something special about sharing your family and your childhood with another girl, creating a connection that shapes who you both become.