The primary meaning of the word satsanga in Hindu religion is the company of
the holy, meaning, association with and becoming one with the supreme Self,
which is of the essential nature of Truth. That means — to remain steady in mental
modification merged in the form of Brahman (brahmakara-vritti). All ignorance
and worldly bondage become annihilated if the mind remains even for a moment in
that mental modification.
The secondary meaning of the word satsang is the company of
holy people, sadhus, who remain meditating on the supreme Self whose essential
nature is Truth.
To study the books written by the great souls who are the knower of Truth, and to read their instructions illuminated by their experiences are also termed sat-sanga.
That is because it is through their instructions that union between the aspirant and the supreme Self, whose essential nature is Truth, can occur.
Srimati T.R. Kanakammal, a direct disciple of the Sri Ramana Maharshi, has heard Him define the true meaning of ‘satsanga’ by saying that the Sanskrit word ‘sat’ means ‘Being’, and the word ‘sanga’ to mean ‘melt’. Thus to seek satsanga is conscious movement within by which we melt into Being!
Source – Notes on Yoga-Vasistha-Sara by Swami Dhireshananda - Swamiji is monk in the Ramakrishna Order