Spam Musubi is a Rice Ball with grilled Spam on top.  The whole thing is wrapped with a strip of Nori seaweed. It is a popular Hawaiian dish but also found in some regions of Japan.

In addition to Onigiri, Musubi or Omusubi is another word for rice ball in Japanese.  Spam meat was a combat ration for soldiers in the American military during World War II.  After Japanese-American soldiers came back to Hawaii after the war, Spam turned into a popular local food when they brought the canned meat with them.  Areas in Japan that have a big American military presence, especially Okinawa, also have a lot of food from the American military after the war, and Spam dishes became popular for restaurant and home food.