Kulam denotes a traditional family who has a  cultural heritage with a strong spiritual background for generations.  Devatha is the God who protects its devotees for their welfare and a prosperous life.  The coined word Kula devatha, hence implies the traditional belief system of a God which is followed by a particular Family.

Kula devatha prayers are believed to be mandatory for the family members. The concept for kula devatha is slightly different from Ishta devatha where in Ishta devatha there is no lineage included.  Like a responsible person, a family is also indebted to have certain commitments to the welfare of the society.  In all these positive contributions to the society, it is the kula devatha, who safeguards the family members to perform their duty in successful manner.
Kula devatha in Kerala is normally the bhagavathi , who is is the assigned family Godess.