|Light is an electromagnetic wave. It can oscillate in any direction that is perpendicular to the direction of energy transport. Polarized light has a preferred orientation of oscillation. Light emitted by a hot object such as a light bulb filament or the Sun is usually oscillating in random directions and is unpolarized. When unpolarized light reflects off something else it can become polarized. Polarized sunglasses work by blocking light that has the same polarization as sunlight reflecting off water and other common reflective surfaces.
If starlight reflects off dust that evenly surrounds it, the polarization vectors would look like the left image. If it reflects off a thin disk the polarization would look like the right image. The polarization pattern of the Beta Pic disk resembles the right image.
Credit: Subaru Telescope