An older sister—a female sibling who is older than oneself. (When referring to someone else's older sister, 'oneesan' is commonly used.)
私の姉は看護師です。
My older sister is a nurse.
休みの日に姉と買い物に行った。
I went shopping with my sister on my day off.
兄と姉が二人いる。
I have a brother and an older sister (two siblings: a brother and a sister).
彼女は自分の姉のことをとても尊敬している。
She respects her older sister very much.