Hi, I would like say that in this link ( ) and starting from 56.28 Suskind tries to find the energy tensor equation using \phi, afterwards he finds a equation similar to wave equation in terms of \phi. My question is: For what does \phi stand ???? I could not capture the meaning of \phi. Could you explain it ???

Well, I am aware that it is a scalar field, but What kind of a scalar field does it stands for ????? This scalar field does not have any name ???? For instance is it a temperature, energy....... ?????

Any scalar field. AFAICT, Susskind is just explaining the general way that the stress-energy tensor of a scalar field works. He is not trying to explain the physics of any particular scalar field. The only property that would have to be assumed is that the field has units of energy density.