Entmoot was the name for a meeting of the Ents of Fangorn Forest, said to be a rare occasion in the later days of the Third Age. The Moot was held by tradition at a dell in the Forest known as Derndingle.
The only Entmoot described in any detail occured between 30 February and 2 March T.A. 3019. Summoned by Treebeard in response to the news brought to him by Meriadoc Brandybuck and Peregrin Took of the Wizard Saruman's treachery, there the Ents decided that -- facing an inevitable slow extinction -- they would attack Isengard to avenge the damage Saruman's Orcs had done to their tree-herds. This so-called '[March of the Ents]' was a significant event in the War of the Ring.