Aranyakas: “forest books” derived from aranya (forest). Aranyakas are theological treatises appended to each Veda. Traditionally, the Aranyakas along with the Upanishads form the jnana-kanda (knowledge section) of the Vedas.

Discussion: The Aranyakas are called forest books because they contain teachings of sages unto their disciples in a forest retreat environment, possibly in the third stage of life, when a person is to live as a forest-dweller (vanaprastha). There are various Aranyaka books appended to different Vedas. In the scheme of the Vedic canon, the Aranyakas form the third set of texts naturally following the Brahmanas (ritualistic texts). The Aranyaka texts contain many prayers, elaboration on Vedic ritual, esotery and mysticism, and sometimes end with an Upanishad. The Taittiriya Aranyaka of the Krishna Yajurveda is especially famous as many prayers used in Hindu temple rituals are derived from this text.

References:
http://en.wikipedia.org/wiki/Aranyaka
http://www.google.com/search?hl=en&q...as&btnG=Search
http://www.gurjari.net/ico/Mystica/html/arayanka.htm
http://www.google.com/search?q=arany...&start=10&sa=N