Honolulu is on the island of Oahu, the second of the four major Hawaiian islands when looking at them from above. The island is the most populated (due to Honolulu) and is the most important island defensively, due to the Pearl Harbor naval base on the North side of the island.

Outside of Honolulu, Oahu's economy is still largely dominated by the tourist sector, with rural resort such as Disney's Aulani serving as major economic draws.

Oahu is the only Hawaiian island to contain a functional passenger railway system (that is not designed for tourists) [see more about the railway here], and has the only passenger airport in Hawaii with more than one runway.          

Fun Fact: Oahu has 5 of Hawaii's 8 Costcos. The rest of the islands only have one each    

Oahu as seen from above. Honolulu is at the bottom-center of the island.