Sight window refers to the area on your bow next to the riser between the top limb pocket and the arrow shelf. It is wear you view your sight when holding the bow at full draw.

Valley refers to the back portion of the draw cycle (when you are drawing your bow) where the draw weight drops off significantly. For example, a 70 lb bow with 80% letoff would be holding around 14 lbs at the bottom of the bow's valley.

I am sure someone can pull a more technical explanation off of one of Norb Mullaney's reports, the huntersfriend website or the Martin website.....