I have heard the word 'VIHITHA KARMA" frequently. What is the real meaning of VIHITHA KARMA. and How does one defines it?
Vihita Karma means karma prescribed or commended by scriptures e.g Vedas. The Sanskrit word Vihita (विहित) can be translated sectioned / prescribed / allowed / commended / enjoined etc. in English. e.g Veda Vihita means prescribed by Vedas.
Here are some translations of verses from Manusmriti that clears it.
वसिष्ठविहितां वृद्धिं सृजेद् वित्तविवर्धिनीम् ।
अशीतिभागं गृह्णीयान् मासाद् वार्धुषिकः शते ॥ ८। १४०
140. A money-lender may stipulate as an increase of his capital, for the interest, allowed by Vasishtha, and take monthly the eightieth part of a hundred.
अकुर्वन् विहितं कर्म निन्दितं च समाचरन् ।
प्रसक्तश्चैन्द्रियार्थेषु प्रायश्चित्तीयते नरः ॥ ११ । ४४
44. A man who omits a prescribed act, or performs a blamable act, or cleaves to sensual enjoyments, must perform a penance.
Bhagavad Gita 17.5: (English translation by Swami Sivananda)
अशास्त्रविहितं घोरं तप्यन्ते ये तपो जनाः।
Those men who practise terrific austerities not enjoined by the scriptures, given to hypocrisy and egoism, impelled by the force of lust and attachment.