As discussed here, Ishwar-Pranidhan is the last of the Niyamas, and is often translated to mean ‘surrender to god.’ When I first encountered this, I thought it strange to refer to a single “God” in a tradition rooted in Hinduism. I cobbled together some definitions in my notes on the subject from 2007 – not sure where I copied these from:
Isvara (Sanskrit) (from the verbal root is to rule, be master):
Lord; the supreme self or hierarch of any universe, large or small, likewise the divine spirit in man. Also a title for many gods in the Hindu pantheon, such as Vishnu and Siva.
In the Bhagavad-Gita Isvara is that which “dwelleth in the heart of every creature” and which “causeth all things and creatures to revolve mounted upon the universal wheel of time” (chs 43; 6l). It is the essence of the spiritual monad in any individualized evolving being, the spiritual root, the god within, and the source of the spiritual and vital streams in any being which bring about its unfolding in evolution and its peregrinations through the fields of experience.
Equivalent to the Father in Heaven of Jesus, and hence the source of the inner Christos or Buddha. Thus in one sense it is the individualized dhyani-buddha of every being.