What Is the Difference Between a Stepsister and a Half-Sister?

A stepsister is the daughter of one's stepparent, while a half-sister shares the same biological mother or father. A half-sister can only share one biological parent to be considered a half-sibling.

If two adults marry, and each has children from a previous relationship, those children will become step-siblings to each other. Neither of the children shares a biological parent.