UpaniShadah

उपनिषद:
(Upanishads)

UpaniShads are concluding portions of Vedas and hence called Vedaanta (the end of the Vedas). The word upaniShad has been held severally to mean: sitting near, devotedly; instructions given by the guru to the disciple sitting close; secret teaching; knowledge of the Absolute.

Each Veda has several branches (shaakaas). Each shaakaa has a karmakaaNDa (which deals with actions to be performed), and mantras. JnaanakaNDa has AaraNyakas (Particularly dealing with studies for those who resort to forest hermitages for devoted and dedicated pursuit of knowledge). UpaniShads are in the AaraNyakas.

Sage Vyaasa had identified 1180 shaakas of the four Vedas. Each shaakaa ends with an upaniShad. Most of upaniShads are lost and only 108 are now available.
Ten of these are called major UpaniShads and are the subjects of commentaries written by all three great Achaaryaas. MuNDakopaniShad has only 13v shlokas but is considered the best.
A commentary (called kaarikaa) was written by GauDapaada (Guru of Shankara's Guru Govindapaada). Shankara has written a commentary on Kaarikaa! BRuhadaaraNyaka and ChaNDOgya UpaniShads are voluminous . The former contains the famous conversation between Yajnavaalkya and his wife Maitreyi. The latter contains a guru-shiShya conversation. Both are illuminating.

Other upaniShads are grouped; Saamaanya (dealing with ordinary matters ), Shaiva, Shakta, Vaishnava, Yoga and Sanyaasa.

Our scriptures comprise 14 Mahaavidyaas.
4 Vedas
6 Vedaangas (Shikshana, Vyaakarana, Chandas, Niruktas, JyotiShya, Kalpa)
4 Upaangas (Meemamsa , Nyaaya, Puraanas and Dharmashaastras)
(PuraaNas have 18 major puraaNas compiled by Vyaasa and two Itihaasas, i.e., RaaamaayaNa and Mahaabhaarata)
(Dharmashaastra includes ManusmRutis)

Upavedas are Aayurveda, Arthashaastra, Dhanurveda and Gandharvaveda (dealing with health, money matters, warfare and dance and arts).