Connolly/Student's Guide, 2. Yoga in the Texts of the Veda

The texts of the Veda (Veda means knowledge) are commonly divided into four groups. The first of these is Samhitā (the four collections of Vedic hymns: the Rg, Yajur, Sāma and Atharva Vedas). The second is Brāhmana (commentaries and interpretations of the hymns along with guidance on the conduct of rituals and some philosophical speculations). Third is Āranyaka (technically 'forest books', for use by brāhmans who had retired to the forest and who wished to conduct alternative versions of the sacrificial ritual). The final group is Upanisad (literally 'sitting down near' the teachers hence 'secret/esoteric teachings that are not to be overheard by eavesdroppers').