Half-sister n. : A sister by one parent only.

Example:
How do I introduce myself to my half sister?

Taxonomy
sibling, Birth order, Sibling rivalry, parents, Foster Siblings, Brothers, Sisters, family, Regressive behavior, sibling relationship, adoptive parents, Articles with unsourced statements, Irish twins, brothers and sisters, free encyclopedia, competition, law, Godparent.

Defination from the web:
sister; that is, any person who shares at least one of the same parents. ... [edit] Half sibling. A half sibling (half brother or half sister) is a sibling with one shared biological or adoptive parent. ...