The elven refuge where the Fellowship forms in J.R.R. Tolkien’s The Lord of the Rings is Rivendell.
Rivendell is the household of Elrond, an important Elven leader and survivor of the First Age. Frodo reaches it after being wounded by a Nazgûl, and Elrond presides over the Council of Elrond there. The council decides that the One Ring must be destroyed rather than used against Sauron, and the Fellowship is formed soon afterward.
In Tolkien’s Elvish languages, Rivendell is also called Imladris, a name often used in the book and by its inhabitants. The refuge lies in a hidden valley east of the Misty Mountains, making it both a sanctuary and a meeting place for representatives of different peoples.
Rivendell is not the same as Lothlórien. Lothlórien is another Elven realm, ruled by Galadriel and Celeborn, which the Fellowship visits after leaving Moria. Mirkwood is a woodland kingdom farther east.