Definitions of jamboree
a large celebration or party, typically a lavish and boisterous one.
the film industry's annual jamboree in Cannes
In Scouting, a jamboree is a large gathering of Scouts who rally at a national or international level.
The 1st World Scout Jamboree was held in 1920, and was hosted by the United Kingdom. Since then, there have been twenty three World Scout Jamborees, hosted in various countries, generally every four years. The 24th World Jamboree is to be held in North America in 2019.
There are also national and continental jamborees held around the world with varying frequency. Many of these events will invite and attract Scouts from overseas.
According to the Canadian Oxford Dictionary, the etymology is "19th century, origin unknown". The Oxford English Dictionary (OED)identifies it as coming from American slang, identifying a use in the New York Herald in 1868 and in Irish writings later in the 19th century. Robert Graves in The Crowning Privilege: The Clark Lectures, 1954–1955 suggests Baden-Powell might have known the word through his regiment's Irish links rather than from the US slang. Poet Robert W. Service used the term well before the first Scouting jamboree. It appears in the poem "Athabaska Dick" in his Rhymes of a Rolling Stone, which was published in 1912. At the time, the word meant a rowdy, boisterous gathering.
Baden-Powell was once asked why he chose "jamboree". He replied, "What else would you call it?" His response made sense if the word had already meant a boisterous gathering. Even so, it is popularly believed within the Scout Movement that the word was coined by Baden-Powell.