Felimath was one of the main Lone Islands (the others being Doorn and Avra_(books)). It was a mostly uninhabited place, described as being a lone green hill in the sea, and was used mainly for keeping sheep.
It was on this island that Caspian, Edmund, Lucy, Eustace and Reepicheep were captured by the slave-trader Pug and his men, and Caspian was purchased by Lord Bern who had been visiting there.