Hidden agenda
Hidden agenda is goal or a need a person or a group is hiding form the rest of the group. The hiding person or group will try to manipulate the decision making process in such a way that their hidden agendas will get high ROI by the group decision and resulting actions. To enter a hidden agenda into the large group consideration the hiding person or group will camouflage the agenda as the group interests.
Mechanism
I suggest that to achieve their hidden goals, people read the minds of other decision makers by "Theory of mind". They try to estimate what their motives, what their understanding of the world, and then enter relevant information to decision making process which will cause the decision makers to deduce decisions in the manipulator's benefit.
Mangers, and especially conservative managers also use hidden agendas to promote their or the organization goals. The more conservative managers are, the less they will use evidence based reasoning, and more local manipulations, to achieve their (sometime hidden) goals. For instance, mangers will dismiss evidences that goes against their line of advancement, and will show them in more convenient interoperation, just to avoid change of their convictions. These manipulations in open communication environment can be traced easily and to be criticized. For this reason, conservative managers prefer to work with close ring of yes-men, and to eliminate any source of critique.
For instance RN which was a senior manger in a board had suggested that a X shouldn't take a job because it is not professional, and very high professionality is needed, where as what she really meant was that this his hear job (and she believed that the job fits her).
One of the most common Hidden agenda is the need to keep your job or to advance into higher position. The first is answering Maslow first level of needs for income that provide the first level of needs, where as the later is answering both the first needs and the fourth need of esteem that come with higher position.
One example is a case that happened on construction of a new building. When one of the employees sow the building plans, he noticed then when ever he will want to get out and smoke he will have to go in front of his boss door. He knew that this will cause the boss to think of him as a lazy worker. To avoid this, he went to the architect office and showed him the design and pointed out that he has not set an emergency door in the office. He told the architect that in a case of fire, the employees will be trapped. The architect immediately recognized his mistake and added a door where the employee wanted. The architect can now feel he protected the employees, and the employee can now go to smoke without his boss noticing it.