Egregore (also spelled Egregor) is an occult concept representing a "thought form" or "collective group mind", an autonomous psychic entity made up of, and influencing, the thoughts of a group of people. The symbiotic relationship of an Egregore and it's group mentality has been compared to the more recent, non-occult concepts of corporations (as a legal entity) and the meme.
The word Egregore come from the Greek word Egregoroi meaning watchers. The result of a synergy of thought could be the closest description of this state of mind. Companies, political parties, religions, prayer groups, states, and clubs all can be said to function under an Egregore. When any project takes on a "mind of it's own", an egregore could be said to be at work, when a common purpose is desired and it has been achieved. For a group of individuals working to produce a particular outcome, an egregore is the desired effect.
However, an egregore can be a negative outcome for a set, who have a weakened mental and emotional state of mental health. It can lead others to harm other individuals for what they believe to be "the greater good of all". Many religious groups like to take advantage of those individuals for whatever personal gain they wish to take from them. Good examples of this would be Jim Jones and the Jones-town Tragedy, David Koresh and the Branch Dividians, Marshal Applewhite and the Heaven's Gate Cult, and Charles Manson, who all used the weakness of others to achieve what lead to the deaths of others by controlling the mental mindset of those entire groups. Jones-town has become known as the largest mass death toll of any tragedy. Those people were convinced by Jim Jones that Armageddon had come, not only willingly committed suicide under his instruction but murdered their own children and those who were reluctant to commit suicide. There are many more examples of how an egregore can be bad but those are some major examples of how one can go terribly wrong.
While one may desire an egregore while working in a group, you must also stress the importance of focusing on the individual as well. The loss of personal self worth is a tragedy. This can also be a dangerous state to reach. Results can vary from suicide to murder. When one individual leads a group, such as a High Priestess, they must be ever aware of the individuals under their tutelage. They must be constantly vigilant to encourage the other members of the group to not only strive for their growth within the group together, but also to put more focus on their own person, individual growth, and development. Group exercises that focus on working independently help to focus on both group and individual development. Meditation and couple workings help strengthen group bonds but also can allow a focus on the individual strengths and weaknesses of each person within the group.
So an egregore can be both good or bad. The abuse of control can sometimes have disastrous effects and lead to a horrible outcome for everyone involved. The founding fathers of the United States realized this when they were forming our government and tried to put into place methods of preventing any one individual from having too much power for too long. For this same reason in covens both a High Priestess and High Priest make joint decisions with the advice of a group of coven elders. As the High Priestess of an eclectic group, I try to focus on everyone's solitary growth and personal learning with guidance.