When the angle of incidence is at the Brewster angle, the reflection coefficient for p-polarized light (light with its electric field parallel to the plane of incidence) becomes zero. This means no p-polarized light is reflected at the interface — all of it is transmitted into the second medium.
At this special angle, the reflected and refracted rays are perpendicular to each other. As a result, the oscillating electric field of the p-polarized light cannot sustain a reflected wave, leading to zero reflection.
However, s-polarized light (with its electric field perpendicular to the plane of incidence) still reflects normally. So, at the Brewster angle, reflected light becomes completely s-polarized, as the p-component vanishes.
This principle is used in devices like polarizing filters and laser optics to eliminate glare or control polarization by taking advantage of this unique behavior at the Brewster angle.