  Out of several possible extensions of general relativity, the scalar-tensor
theory is the most popular for several reasons. Since the quantum description
of gravity is yet to be formulated properly, the understanding of a
gravitational theory remains incomplete until the study of thermodynamic and
fluid-gravity aspects, which provides an alternative viewpoint to understand
the gravitational theory. In this review, we study these features
(thermodynamics and the fluid gravity analogy) in a rigorous and yet in a
concise manner for the scalar-tensor gravity, which has been revealed in our
recent works. In addition, the issue of conformally connected frames
(\textit{i.e.} whether the two frames, which are conformally related are
physically equivalent) has been explored in an explicit manner at the action
level as well as from the viewpoint of thermodynamics and fluid-gravity
correspondence.
