What is "landdisir"

In Norse mythology and later Icelandic folklore, landdísir ( Old Norse " dísir of the land") are beings who live in landdísasteinar, specific stones located in Northwestern Iceland which were treated with reverence into the 18th and 19th centuries. The landdísir are not recorded in Old Norse sources, but belief in them is assumed from the name landdísasteinar.