Actually the word Vedanta is the synonym of Upanishads. The main holy scripture of Hinduismis Veda. In fact Veda means knowledge – to know everything worldly and spiritually The Veda is of four parts. Such as:
i)  The Rikveda (with 10,472 hymns)
ii)  The Shumveda (with 1,810 hymns)
iii)  The Yajurveda(with 1,915 hymns)
iv)  The Atharbaveda(with 6,000 hymns)
Upanishad is the collection of all purports and discussions of Vedas uttered by different saints (composers of Vedic hymns).

The word- Upanishad is a word of Sanskrit language. This word is divided into two parts –  ‘Upa’ which refers to – to seat in front of preceptor (teacher of spiritual knowledge)  and ‘Nishad’ which refers to  – to gain supreme knowledge. So, Upanishad means fully – to gain supreme knowledge being closest to a good preceptor. For being the last part of Vedas, it is called Vedanta. Vedas have two sides, first one is ‘Philosophy’ and another is ‘Tantra’- a scripture of methods of prayers and worships.

        A few quotations of Genius about Upanishad-

  • Upanishad is mysterious knowledge.  -( Dr.Deusen, Philosophy of the Upanishads, P-14-15)
  • For gaining knowledge sitting close to a preceptor, it is called Upanishad.  –( Maxmuller).