Dichroism and the Wire-Grid Polarizer
Dichroism is the propensity of an optical system to selectively transmit (or absorb) one of the orthogonal P-states in a beam of light.
Watch the following video explaining 'un-polarized' light, wire grid polarizers, and Polaroid film
How polarising filters work? (video, approx. 14:32 mins, CC)
The important thing for wire grid polarizers is that the transmission axis is perpendicular to the wires. This is explained well in the video above.
Beware, other sources DO GET THIS WRONG!