Half-sister

Somebody's half-sister is a female sibling with one shared parent.

While many half-sisters are step-sisters and vice versa, someone may have either relationship without the other: step-siblings each have a parent married to a parent of the other but not necessarily a parent in common, and half-siblings not living in the same household are not always considered step-siblings.

See also: family, sister, half-brother, illegitimacy.