An aviator is a pilot. Every aircraft you see in the sky has an aviator in it. Aviation is the science that makes airplanes and other vehicles that fly through the air. An aviator is someone who flies one of those vehicles.
Aviator style sunglasses are intended to be worn under headgear and are characterised by dark, oftentimes reflective lenses and thin monel, steel or titanium metal frames with double or triple bridges and bayonet earpieces or flexible cable temples that hook more securely behind the ears.
Cassie was a great character, as she was adamant in figuring out the cause of her dad's death, even when the authorities brushed it off as a mere accident. She never appeared again and was never mentioned again, even though she is still alive.
While Rory moves on from Jess in Seasons 4 and 5, they have reunions in Season 6 where Jess is doing well, and in the revival, they have a good and peaceful friendship.