or seat back
the back support of a seat in an aircraft, motor vehicle, etc.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for seatback
Historical Examples of seatback
And old Judge Priest came with him, and both of them lunged forward over the seatback at the ruffian, three feet away.Back Home
Irvin S. Cobb