The O2 Arena, commonly known as the O2, is a multi-purpose indoor arena in the center of the O2 entertainment complex on the Greenwich Peninsula in southeast London. It opened in its present form in 2007. It has the second-highest seating capacity of any indoor venue in the United Kingdom, behind the Manchester Arena, and in 2008 was the world’s busiest music arena. As of 2022, it is the ninth-largest building in the world by volume.
The arena was built under the Millennium Dome, a large dome-shaped building built to house an exhibition celebrating the turn of the third millennium; as the structure still stands over the arena, The Dome remains a name in common usage for the venue. The arena, as well as the overall O2 complex, is named after its primary sponsor, the telecommunications company O2, a subsidiary of Virgin Media O2. Wikipedia