Edible seaweed (nori), usually dried and pressed into sheets used for sushi, rice balls, etc.
おにぎりに海苔（のり）を巻いて食べる。
I wrap rice balls with nori and eat them.
寿司の上にのりを使うことはあまりないが、巻き寿司には欠かせない。
Nori isn't often used on top of sushi, but it's essential for maki (rolled sushi).
韓国では紫菜（のり）をスープやおやつに使うことも多い。
In Korea, nori (gim) is often used in soups and snacks as well.