Lindon is the land beyond the Ered Luin (Blue Mountains) in the northwest of Middle-earth. It is the westernmost land of the continent. The Gulf of Lune divides it into Forlindon (North Lindon) and Harlindon (South Lindon).
Lindon as a name survived from the First Age, when it was a name given to Ossiriand after this land was settled by the Laiquendi or Green Elves. Lindon meant "Land of the singers", after the old name Lindar (singers) for the Teleri.
Lindon is the last mainland remnant of Beleriand left after the War of Wrath at the end of the First Age, the rest of the land having been broken or submerged by the tumults. While not exactly clear, there are indications that before the Downfall of Númenor Lindon was larger than it was during the Third Age.
Many of the Elves of Beleriand relocated to Lindon at the beginning of the Second Age, where they were ruled by Gil-galad. The Noldor mainly dwelt in Forlindon, and the Sindar (and surviving Laiquendi) in Harlindon. Together, they built Mithlond (the Grey Havens) on the Gulf, and many Elves left from there to Valinor. Lindon was one of the two Noldorin Kingdoms during the Second Age (the other being Eregion or Hollin), until Gil-galad was killed by Sauron during the War of the Last Alliance of Elves and Men. After that, most of the Ñoldor finally departed for Valinor, and Lindon became depopulated, now ruled by Gil-galad's lieutenant, the Sindarin elf Círdan the Shipwright, who kept building ships for the departing Elves.
In the literature, Lindon itself appears mostly as a place where reluctant Elves tarried before departing forever from Middle-earth.