Upanishads are the philosophical description of Vedas. Different Rishi’s (Sage’s) have explained the Vedas
As there are four Vedas, Each Vedas have their Upanishads. So, They are called Vedanta also. The exact number of Upanishads is not known, some popular Upanishads are tabulated on this page. According to the Vedic studies,
The Rigveda have 10 known Upanishads and Samveda have 16.
Yajurveda have 50 known Upnishad. and Atharvaveds have 32 Veda.