About the title:
Technically, it can refer to Selidor, the westernmost island of Earthsea, and historically significant for being the place where Erreth-Akbe perished while fighting the dragon Orm. It is so distant from most of the archipelago, that in parts of Earthsea, fairy tales begin with the phrase "As long ago as forever, and as far away as Selidor...." It was also known (to Sparrowhawk, anyway) as the lair of Orm Embar, and the place where Orm Embar revealed to him how the Lost Rune of the Kings (and the Ring of Erreth-Akbe) could be found. Geographically, the climax of the novel takes place when Sparrowhawk and Arren reach the westernmost cape of the westernmost island-- literally, the farthest shore (beyond which there is no land). Thematically, the novel's choice to focus on the west balances the first novel's climax in the farthest known seas of the east.
The title also figures in an Earthsea prophecy: The last king of Earthsea, Maharion, dead now for eight centuries, said that "He shall inherit the throne who has crossed the dark land living and come to the far shores of the day." A cryptic prophecy, to be sure, since the only living beings to enter the dark land (the land of the dead) are mages, and they report only one way in and out-- they've never "crossed" it.
Originally the last novel of a trilogy
, after a 2 decade hiatus, Ursula K. LeGuin
wrote a sequel
, that mostly deals with the aftermath
of The Farthest Shore