(covers information from several alternate timelines)
A tribunal is a court of justice.
In 2259 of the alternate reality, after a mission to Nibiru in which the indigenous population saw the USS Enterprise – an action which violated the Prime Directive, Admiral Alexander Marcus convened a special tribunal to investigate the conduct of Captain James T. Kirk. Admiral Christopher Pike, a mentor and friend to Kirk, was not invited. The tribunal ruled against Kirk and ordered that he be stripped of his command and sent back to Starfleet Academy for further training. (Star Trek Into Darkness)