Polarization
Definition
Filtering light so its waves vibrate in only one direction — how polarized sunglasses kill glare.
Technical definition
The restriction of a transverse wave's oscillations to a single plane. Unpolarized light (e.g., sunlight) vibrates in all directions perpendicular to travel; a polarizer transmits only one component, following Malus's law I = I₀cos²θ.
Example
Glare off a wet road is mostly horizontally polarized light. Polarized sunglasses block that horizontal component while passing vertical light — the road's blinding shimmer vanishes but the scene stays bright.
Only transverse waves can be polarized. Sound — a longitudinal wave — cannot be polarized at all, because its vibrations run along the travel direction with no 'sideways' to filter. This is actually proof that light is transverse: the very existence of polarized light rules out a longitudinal light wave.