The flag of Oman is three horizontal bands of white, red, and green with a red stripe down the hoist, and the national emblem set into the upper hoist corner.
Qaboos and the redesign
Everything about the modern flag dates from 1970, the year Sultan Qaboos bin Said came to power, unified the country and began the modernization program that defined his reign. The plain red banner Oman had used until then said little that other flags in the region did not also say. The first version of the new flag used different proportions: the middle red stripe was narrower than the white and green ones above and below it. On April 25, 1995 the three stripes were made equal in width and the shape of the flag changed, and a royal decree of May 22, 2004 fixed the current specification, including the 4:7 proportions and the exact shades of red and green.
Oman's earlier flags had shifted with its politics, as they tended to for a country whose history is one of maritime empire and trade.
The khanjar and the three colors
White is peace and prosperity. Red is the long struggle against foreign domination. Green is fertility and, specifically, the Jebel al-Akhdar, the Green Mountains, and the agriculture that goes with them.
The emblem inside the vertical red stripe is a khanjar, the traditional Omani dagger, with two swords crossed behind it. Both are old symbols of Omani identity, and they are on the flag for strength and bravery rather than for any single event.
Where it flies
The flag is flown on government buildings, embassies, and public institutions, and it appears at state functions, military parades, and national holidays under the usual protocols for handling and display. There is also a naval ensign, which follows international maritime convention.
Red runs through the flags of most of Oman's neighbors on the Arabian Peninsula, a shared inheritance from the region's history and its resistance to outside control. Oman's flag sits in that family without being mistakable for any of the others.
References
[1] Oman Ministry of Heritage and Culture - Flag of Oman https://www.mhc.gov.om/Flag
[2] The Flag Institute - A Guide to Oman's Flag https://www.flaginstitute.org/flags/oman
[3] Encyclopaedia of Middle Eastern History - Oman and Its Symbols
[4] World Vexillological Research Institute - National Emblems of Oman
[5] Books on Middle Eastern History - The Unification of Oman