Nickname: The Gathering Place
|Location||21°28′23″N 157°59′12″W / 21.4730°N 157.9868°W|
|Area||596.7 sq mi (1,545 km2)|
|Area rank||3rd largest Hawaiian Island|
|Highest elevation||4,025 ft (1226.8 m)|
|Pop. density||1,704/sq mi (657.9/km2)|
Oahu ( /oʊˈɑːhuː/) ( Hawaiian: Oʻahu (pronounced [oˈʔɐhu])), also known as "The Gathering Place", is the third-largest of the Hawaiian Islands. It is home to roughly one million people—over two-thirds of the population of the U.S. state of Hawaii. The island of O’ahu and the Northwestern Hawaiian Islands constitute the City and County of Honolulu. The state capital, Honolulu, is on Oʻahu's southeast coast. Oʻahu had a population of 995,638  according to 2022 U.S. census estimates, up from 953,207 in 2010 (approximately 70% of the total 1,455,271 population of the state of Hawaii,  with approximately 81% of those living in or near the Honolulu urban area).
The Island of Oʻahu in Hawaii is often nicknamed (or translated as) "The Gathering Place". It appears that Oʻahu grew into this nickname; it is now the most populous Hawaiian Island, but in ancient times was not populous and was outranked by the status of other islands. The translation of "gathering place" was suggested as recently as 1922 by Hawaiian Almanac author Thomas Thrum. It has been speculated[ by whom?] that Thrum ignored or misplaced the ʻokina because the Hawaiian phrase "ʻo ahu" could be translated as "gathering of objects" (ʻo is a subject marker and ahu means "to gather"). The term Oʻahu has no confirmed meaning in Hawaiian, other than that of the place itself.  
The city of Honolulu—the state's largest city, capital, and main deepwater marine port—is here. As a jurisdictional unit, all of Oʻahu is in Honolulu County, although Honolulu occupies only part of its southeastern end.
Well-known features of Oʻahu include Waikiki, Pearl Harbor, Diamond Head, Hanauma, Kāneʻohe Bay, Kailua Bay, North Shore, and the resort destination Ko Olina.
While the island is designated the City and County of Honolulu, excluding the minor Northwestern Hawaiian Islands, residents identify settlements using town names (generally those of the census-designated places), and consider the island divided into various areas that may overlap. The most commonly accepted areas are the "City", "Town" or "Town side", which is the urbanized area from Halawa to the area below Diamond Head (residents of the island north of the Koʻolau Mountains consider the Town Side to be the entire southern half), "West Oʻahu", which goes from Pearl Harbor to Kapolei, ʻEwa and may include the Waiʻanae and Mākaha areas; the " North Shore" (northwestern coast); the " Windward Side" (northeastern coast from Kahuku to Kāneʻohe); the "East Side" or "East Coast" (the eastern portion of the island, from Kāneʻohe on the northeast, around the tip of the island to include much of the area east of Diamond Head); and "The Valley" or "Central Oʻahu", which runs northwest from Pearl Harbor toward Haleʻiwa.[ citation needed] These terms are somewhat flexible, depending on the area in which the user lives, and are used in a general way, but residents of each area identify strongly with their part of the island, especially those outside of widely known towns. For instance, if asked where they live, a local would usually reply "Windward Side" rather than " Kailua".[ citation needed]
The island has been inhabited since at least the 3rd century A.D.  The 304-year-old Kingdom of Oʻahu was once ruled by the most ancient aliʻi in all of the Hawaiian Islands. The first great king of Oʻahu was Maʻilikūkahi, the lawmaker, who was followed by many generations of monarchs. Kualiʻi was the first of the warlike kings and was succeeded by his sons. In 1773, the throne fell upon Kahahana, the son of Elani of Ewa. In 1783, Kahekili II, King of Maui, conquered Oʻahu, deposed the reigning family, and made his son, Kalanikūpule, king of O'ahu, turning O'ahu into a puppet state. Kamehameha the Great conquered Kalanikūpule's forces in the Battle of Nuʻuanu. Kamehameha founded the Kingdom of Hawaiʻi with the conquest of Oʻahu in 1795. Hawaiʻi was not unified until the islands of Kauaʻi and Niʻihau surrendered under King Kaumualiʻi in 1810. Kamehameha III moved his capital from Lāhainā, Maui to Honolulu, Oʻahu in 1845. ʻIolani Palace, built later by other members of the royal family, still stands, and is the only royal palace on American soil.
Oʻahu was apparently the first of the Hawaiian Islands sighted by the crew of HMS Resolution on January 19, 1778, during Captain James Cook's third Pacific expedition. Escorted by HMS Discovery, the expedition was surprised to find high islands this far north in the central Pacific. Oʻahu was not actually visited by Europeans until February 28, 1779, when Captain Charles Clerke aboard HMS Resolution stepped ashore at Waimea Bay. Clerke took command of the ship after James Cook was killed at Kealakekua Bay ( island of Hawaiʻi) on February 14, and was leaving the islands for the North Pacific. With the discovery of the Hawaiian Islands came the introduction of disease, mosquitoes, and aggressive foreign animals. Although indirect, simple exposure to these foreign species caused permanent damage to the Native Hawaiian people and environment.
The Imperial Japanese Navy's attack on Pearl Harbor, Oʻahu on the morning of December 7, 1941, brought the United States into World War II. The surprise attack was aimed at destroying the American will to fight and making them sue for peace immediately by attacking the Pacific Fleet of the United States Navy and its defending Army Air Forces and Marine Air Forces. The attack damaged or destroyed 12 American warships, destroyed 188 aircraft, and resulted in the deaths of 2,335 American servicemen and 68 civilians (of those, 1,177 were the result of the destruction of the USS Arizona alone).
Today, Oʻahu has become a tourism and shopping haven. Over five million visitors (mainly from the contiguous United States and Japan) flock there every year.
Oʻahu is also known for having the longest rain shower in history, which lasted 200 consecutive days. Kāneʻohe Ranch reported 247 straight days of rain from August 27, 1993, to April 30, 1994. The average temperature in Oʻahu is around 70–85 °F (21–29 °C). The island is the warmest from June through October. The winter is cooler, but still warm, with an average temperature of 68–78 °F (20–26 °C).
Oʻahu is 44 miles (71 km) long and 30 miles (48 km) across. Its shoreline is 227 miles (365 km) long. Including small associated islands such as Ford Island plus those in Kāneʻohe Bay and off the eastern ( windward) coast, its area is 596.7 square miles (1,545.4 km2), making it the 20th-largest island in the United States.  The windward side is known for some of the world's most beautiful beaches. Lanikai Beach on the windward coast has been consistently ranked among the world's best beaches.  The island is composed of two separate shield volcanoes: the Waiʻanae and Koʻolau Ranges, with a broad valley or saddle (the central Oʻahu Plain) between them. The highest point is Kaʻala in the Waiʻanae Range, rising to 4,003 feet (1,220 m) above sea level. 
Being roughly diamond-shaped, surrounded by ocean, and divided by mountain ranges, directions on Oʻahu are not generally described with compass directions. Locals instead use directions with Honolulu as the central point. To go ʻewa means toward the western tip of the island, "Diamond Head" is toward the eastern tip, mauka is inland (toward the central Koʻolau Mountain range, north of Honolulu) and makai toward the sea. When these directions became common, Diamond Head was the eastern edge of the primary populated area. Today, with a much larger populace and extensive development, the mountain is often not actually to the east when directions are given, and is not to be used as a literal point of reference—to go "Diamond Head" is to go to the east from anywhere on the island.
Beginning with a contract with the US Navy in 2001, Ocean Power Technologies began ocean-testing Azura, its wave power generation system at the Marine Corps Base Hawaii (MCBH) at Kāneʻohe Bay. The Oʻahu system was launched under the company's program with the US Navy for ocean testing and demonstration of such systems, including connection to the Oʻahu grid.  The prototype can produce 20 kW, a system with 500 kW to 1 MW is planned to be installed at end of 2017. 
Oʻahu has 343 MW of rooftop solar power,  and potential for 92 MW of wind power.