What is the phisical significance of dipol moment .?

Question

why does it directed from negative to positive charge?

Answer 1

The electric dipole moment is sort of like a moment of force, but for charge.  Imagine a pure dipole (which is like a couple).  You have a positive and a negative part separated by some distance.  In an E-field that isn't parallel to the dipole, the electric forces pull the positive charge one way and pull the negative charge the other way, and thereby exert a torque on the dipole.  And you can calculate much more calculated interactions than that--between 2 dipoles, etc.

The direction of the dipole moment vector goes negative to positive by convention.  You have to have it point some way and that choice is mathematically simplest.