The Olympic Cauldron is the structure that is lit by the Olympic Torch at the end of the torch relay and opening ceremony of that particular Olympiad. Its design is up to the discretion of the host country's Olympic committee and often looks quite a bit different than a traditional cauldron. In addition, the process of lighting it is special in its own way as a different method is usually utilized at each Games; some examples being a fiery arrow shot in a arc into the cauldron and the final torch bearer of the relay being lifted up by a harness to the location of the cauldron.
The only requirement placed upon the creation and positioning of the structure is that it is in the open air of the host city, though as demonstrated at the 2010 Winter Olympic Games in Vancouver, a torch can be lit both inside and out. or it must be inside and has a live video feed about the situation like on London 2012.