Between the Brahmanas and Upanishads are a few secondary texts. These are called Aranyakas or Forest texts to be used by those who left society to reside in the forest to gain spiritual knowledge (Vanaprasthas). The Aranyakas do not give us rules for the performance of sacrifices and explanations of the ceremonies, but provide us with mystic teaching of the sacrificial religion.
Since the Aranyaka texts are a part of the Vedas, they too are considered shruti. They are religious and philosophical writings that explain abstract concepts like the mystical aspects of ceremonies and the nature of god.
The Aranyakas were composed around 700 - 600 BC, much later than the Brahmanas. They are treaties for hermits and sages who concentrate on meditation and asceticism, after having retired from worldly distractions to the forest (see also Ashram). These texts interpret the sacrificial rites and rituals explained in the Brahmanas in metaphysical and cosmic terms, giving the logical reasons for their practice.
Most Brahmanas have one or more Aranyakas associated with them. For example, the Aitareya and Kaushitaki Aranyakas are associated with the Aitareya and Kaushitaki Brahmanas of the Rig-Veda. There are no Aranyakas associated with the Atharva Veda.