Roasted Seaweed is called Sushi Nori or Yaki Nori in Japanese. It is used for rolled sushi such as California Roll and Hand Roll Sushi. Roasted Seaweed has a mild but distinctive seafood flavor. It is thin and crisp when it’s dry, but somewhat chewy when moistened.
Roasted Seaweed is dried and roasted seaweed which is made into a paper like form, perfect to hold rice and fillings. Roasted Seaweed for sushi is usually sold as 8″ x 8″ squares. The sheet has a front side and a back side. The shiny side is the front which should be on the outside of sushi rolls. You may find much smaller or rectangular seaweed, Ajitsuke Nori, which is already seasoned. While that is not really suitable for sushi rice, it can work well with food using regular rice, like Onigiri. There is also conveniently-already-shredded Kizami Nori, and that can be used as a topping for various dishes like salads and noodles. There are soy papers that are alternative to Roasted Seaweed, but the flavor is not exactly the same.
Roasted Seaweed is found at most US supermarkets in the Asian food aisle, but if not, it can easily be found online.