What's the coordinate ability?
Titans can have different types of abilities, like shifting back to human form (aka Titan Shifters), or putting armor on themselves (eg: Armored Titan, Annie hiding the back of her neck, ...). The third ability that was shown, was that of the Coordinate.

The Coordinate ability is basically the ability to control Titans. If the ability is controlled properly it can command all Titans to do whatever you want them to do.


   This is how humans were able to built the walls as sturdy and as big as they are right now.


As far as the story goes, it does not seem to work on Titan Shifters and there is supposed to be only one Titan with the Coordinate ability.


   Although the Beast Titan was shown to have a similar ability.