Druidic Grand Keeper

Druidi Grand keeper is a person who is often the head of a druidic, or similar circle. For example, a grandkeeper of the The Windkeepers is one of the druidic leaders of the loosely knitted organization in question. In some cases they are not a druid, but more often than not they are. This is not a requirement, though, but the veneration is: they need to be respected by their people as the ultimate and highest form of authority in their group. This also applies to other  not solely druidic circles like the wavekeepers or the windkeepers.
Sometimes The Druidic Grand keeper, or more commonly known ust as the Grand Keeper or The Keeper, can be mixed with certain other titles like The Grand Keeper of Ivaeharaith, who is not a druid but basically the highest ranking archivist and librarian in the elven city-state Ivaerenor. Usually one can easily tell the difference by the context, though.

Requirements

To become a Grand Keeper, one most be the most venerated person in their group of practitioners. They lose their status when they lose the veneration or cannot hold up to the task of leading or protecting anymore. Previous Grand Keepers are still often highly revered, even when they retire, if they have done their job well.

Alternative Naming

The Great Wind, Wave, Tree etc, depending on the druidic circle/group

Equates to

The Grand Keeper is the most senior druid and thus the leader of their tribe or druidic circle. There is no one higher than the forces and deities of Natural world above them.

Source of Authority

Seniority. Usually the Grand keeper is the oldest and thus, often the most skilled in their group. This is not always the case, though.

Length of Term

As long as the others regard them the Grand Keeper, they also are that. They lose their status when they lose their group's veneration or they retire, passing the baton to the next one..