From The Heretic Knowledge Vault
A rank in the elven military, and probably in others as well; superior to garden-variety Commander, no doubt. The only character yet identified as a High Commander is one Yenhael, who's invoked when Sarine, Jon and Sara trek to Praenubilus Astu to try to rescue the Errant-napped Meji, and again when Sarine and the Amraphels address the Elven Council. Interestingly, the High Commander himself doesn't seem to be in the council chambers for this historic moment, and the elven military is represented instead by the lower-ranking Commander Nisotta. We don't know why.
The High Commander does seem to wield real influence, however. He and Nisotta consulted with the Great Houses (or presumably their representatives) to decide whether to exchange Meji for Peregin Barin, who's being held hostage in Tsuirakushiti until the elves return Meji to her family. For the moment, they've decided not to make the exchange, but rather to squeeze Meji for as much intelligence on Anilis and Ian Samael as they can manage. This is probably a military (at least "elven" military) way of thinking, and most definitely a mistake...