Sticky bit
The "sticky bit" is bit 6 of the words stored in the Sprite Control Bank 3. Setting it to 1 makes the corresponding sprite "stick" to the precedent one.
The video hardware will automatically add 16 to its current X position, and use the same Y position, size and vertical shrink coefficient. Only the horizontal shrink coefficient is left independant.
Sticky sprites can also be called "driven sprites".