Oahu () (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—about two-thirds of the population of the U.S. state of Hawaii. The island is within Honolulu County and the state capital, Honolulu, is on Oahu's southeast coast.
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.Oahu is 44 miles (71 km) long and 30 miles (48 km) across. Its shoreline is 227 miles (365 km) long. The island is composed of two separate shield volcanoes: the Waiʻanae and Koʻolau Ranges, with a broad valley or saddle (the central Oahu Plain) between them. The highest point is Kaʻala in the Waiʻanae Range, rising to 4,003 feet (1,220 m) above sea level.The island, which is also Honolulu County, has a July 1, 2019 population estimate of 974,563 (up from 953,207 people in 2010 (approximately 69% of the total 1,415,872 population of the state, with approximately 81% of those living in or near the Honolulu urban area)). Oahu has for a long time been known as the "Gathering Place". The term Oʻahu has no confirmed meaning in Hawaiian, other than that of the place itself. Ancient Hawaiian tradition attributes the name's origin in the legend of Hawaiʻiloa, the Polynesian navigator credited with discovery of the Hawaiian Islands. The story relates that he named the island after his daughter.
Residents of Oahu refer to themselves as "locals" (as done throughout Hawaii), no matter their ancestry.
There are three federal freeways, all part of the Interstate System, on Oahu: H1, H2, and H3. H1 runs from Ewa (Leeward side) to Honolulu, where it turns into the Kalanianaʻole Highway. H2 and H3 branch off H1 to take drivers to the North Shore and Windward side, respectively.
The city of Honolulu—largest city, state capital, and main deepwater marine port for the State of Hawaiʻi—is located here. As a jurisdictional unit, the entire island of Oahu is in the Honolulu County, although as a place name, Honolulu occupies only a portion of the southeast end of the island.
Well-known features found on Oahu include Waikiki, Pearl Harbor, Diamond Head, Hanauma, Kāneʻohe Bay, Kailua Bay, North Shore, and the resort destination, Ko Olina.
While the entire island is officially the City and County of Honolulu, locals identify settlements using town names (generally those of the census-designated places), and consider the island to be divided into various areas, which 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 Oahu", which goes from Pearl Harbor to Kapolei, ʻEwa and may include the Mākaha and Waiʻanae 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 Oahu" which runs northwest from Pearl Harbor toward Haleʻiwa. These terms are somewhat flexible, depending on the area in which the user lives, and are used in a mostly 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 locals are asked where they live, they would usually reply "Windward Oahu" rather than "Laie".
Being roughly diamond-shaped, surrounded by ocean and divided by mountain ranges, directions on Oahu are not generally described with the compass directions found throughout the world. Locals instead use directions originally using Honolulu as the central point. To go ʻewa means traveling 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 itself 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.
Oahu is also known for having the longest rain shower in history, which lasted for 200 consecutive days. Kāneʻohe Ranch reported 247 straight days with rain from August 27, 1993 to April 30, 1994. The island has many nicknames one of them being "rainbow state." This is because rainbows are a common sight in Hawaiʻi due to the frequent rain showers. The average temperature in Oahu is around 70–85 °F (21–29 °C) and the island is the warmest in June through October. The weather during the winter is cooler, but still warm with an average temperature of 68–78 °F (20–26 °C).
The windward side is known for some of the most beautiful beaches in the world. Lanikai Beach on the windward coast of Oahu has been consistently ranked among the best beaches in the world.