Polarization
Polarization is when light waves line up to move in only one direction.
Think of it this way
A window blind has slats that run across it. Light coming through can only pass when the slats line up with it. Turn the slats sideways, and the light is blocked. Polarized light works the same way — a filter only lets through waves moving in one direction.
Explaining polarization by grade level
Put on a pair of sunglasses and look at a bright window. The glare goes away. Those lenses only let light moving one way pass through. Light moving other ways gets blocked. That is how the glasses cut the bright shine.