What is Seatback?
1.
When leaving a chair, you can say "I call seatback" and no one else in the room can take the seat away from you. Similar to saying, "I call shotgun" when approaching a car.
No way, you can't sit there, I called seatback!"
See
2.
The action of accidentally leaving something behind on an airplane, most notably in the seatback storage area in front on you.
I was reading a great article in Wired, but I seatbacked it on the flight back from Kona.