Short answers, pulled from the story.
The Council of Elrond is the second chapter of Book 2 of J. R. R. Tolkien's The Lord of the Rings, published in 1954-1955. It is the longest chapter in the book at roughly 15,000 words, and it serves as the narrative moment where the threat of the One Ring is fully explained, the final members of the Fellowship are introduced, and the quest to destroy the Ring in Mount Doom is agreed upon.
The chapter consists almost entirely of people talking, with the action narrated in flashback rather than shown directly. Tolkien scholar Tom Shippey calls it "a largely unappreciated tour de force" precisely because, in a chapter of 15,000 words with twelve speakers present and seven more quoted within Gandalf's speech alone, very little happens in the present tense, yet the chapter never loses the reader's attention.
Twelve characters speak during the Council itself, including Elrond, Gandalf, Boromir, Aragorn (revealed as the heir of Isildur), Gloin the Dwarf, Legolas, and Bilbo Baggins. Gandalf's speech is the longest, occupying roughly half the chapter, and within it he quotes or paraphrases several additional voices including Saruman and the Gaffer Gamgee.
Fleming Rutledge, an Episcopal priest and Tolkien scholar, writes that the chapter brings the hidden Christian narrative of The Lord of the Rings almost explicitly to the surface. She describes it as "replete with theological meaning," citing Dain II Ironfoot's refusal of Sauron's offered Dwarf-Rings as heroic resistance to temptation, and Elrond's remark that "nothing is evil in the beginning, even Sauron was not so" as central to the book's moral argument.
Jackson moved the history of the Ring from the Council scene to a voiced-over prologue at the start of his 2001 film The Fellowship of the Ring, dramatically shortening the Council scene itself. Film scholar Judith Kollmann notes that Jackson also shifted the scene's focus from Frodo to Aragorn, replaced Tolkien's calm, systematic debate with a heated argument, and showed Frodo and Sam with bags already packed rather than arriving at their decision through the weight of deliberation.
Tom Shippey describes the Council of Elrond as paralleling the house of Beorn in The Hobbit, in that both chapters stage a collision between the ancient heroic world and the practical modern world. The Council is, in Shippey's assessment, many times more complicated than the Beorn chapter, and it marks the point after which Tolkien was no longer writing his way through territory he had explored in The Hobbit.