A cushion attached to the back of a saddle for an additional passenger
a seat behind the rider of a horse or motorbike etc.
A pillion is a mostly British English term for a secondary pad, cushion, or seat behind the main seat or saddle on a horse, motorcycle, or moped. A passenger in this seat is said to "ride pillion" or may themselves be referred to as a "pillion. ...
Pad or cushion attached to the rear of a saddle for a second person to ride.
seating for a passenger behind a motor cyclist.
refers to a passenger on the back of the motorcycle, or can also mean a small cushion seat which is designed for use by the pillion passenger.
This one can mean either a passenger riding on the back of the bike or the back seat itself.