Nori is dried, paper thin sheets of seaweed used as the outside "wrapper" for many types of sushi. In addition to a common sushi ingredient it can also be served lightly toasted as a breakfast food. Store in an airtight bag, indefinitely.
Nori can be purchased in many well stocked stores such as Trader Joe's, Whole Foods and many main stream grocery stores. You can purchase nori online as well on sites such as Amazon.com.
For people with certain allergies, or people who simply don't like Nori you can substitute soy bean paper (Mamenori). The soy bean sheets come in various colors, all have a neutral flavor. Read more about soy bean paper. See other possible substitutions above.