The tiller is the handlebar assembly where the dash and the steering assembly are. Tillers are columns that you can use to steer the Mobility Scooter and locate the controls such as forward/reverse, speed, and turning signals. Some are height adjustable and some can tilt forward or backward.
An articulating tiller is also known as a tilt-adjustable tiller. This allows the user to bring the handlebar assembly (aka tiller) closer or further away from the user. One example of a Mobility Scooter where the tiller is tilt-adjustable is the Baja Wrangler 2.