what do they mean when sunglasses are Polarized? and what are dark lens callled?

Answer 1

polarized glasses are treated so that when you look at water, you will not see a sun glare.

Answer 2

The lenses are treated to only let light through where the waves are travelling in one direction, reducing glare. You can check this out by putting one polarized lens on top of another, rotated 90 degrees. No light will pass through.