Founding Titan (Anime)

The Coordinate (座標) is an incredible power over the Titans which is being sought after by the warriors. As suspected by the warriors, it is currently held by Eren Jaeger.

Clash of the Titans arc
Before fleeing the Scouts in the Forest of Giant Trees, Reiner states that the connections between the Reiss family and the Order of the Walls make Historia Reiss a valuable asset for the warriors' mission, and having her with them will make their goal much easier if Eren Jaeger is not the "Coordinate" they are searching for.

Later that day, the warriors' suspicions are confirmed when Eren unleashes the Coordinate, striking the hand of a smiling Titan and causing all the surrounding Titans to swarm it and tear it to pieces.