As per Monier williams on line dictionary
http://www.sanskrit-lexicon.uni-koeln.de/monier/
one of the meaning is "to explain".
It is the meaning and intrepretation of religious texts. That is what our Upanyasa pundits do. Sengalipuram Ananda Rama Dikshidar and Kripananda Warier were two of the famous Upanyasam people.
This is a long standing tradition in Tamil Nadu. It used to be held in temples. It has moved to public halls now.
It is there in other states also. In Hindi it is called Pravachan. You could call them spritual lectures. The most famous exponent today in Hindi is Ashramji.