Postby javiskefka » July 15th, 2008 6:35 pm
자매 specifically means "sisters". It's composed of the hanja for "older sister" and "younger sister". You can use it to refer to a pair of sisters, or to talk about a sisterly relationship.
There's a similar word for brothers, 형제, but this one can also be gender-neutral "siblings" or members of the same faith community.