Transgression means that an action, contemplation, or end result has gone directly against a character’s belief (Code of Conduct, tenets of faith, etc.). Typically both direct and indirect results count as a transgression – depending on whether the such beliefs are adhered to in both letter and spirit. A transgression is an affront to the deeply held beliefs and represents opposition to them.
Transgression against others beliefs can result in some sort of proclamation against the transgressing entity by civil, religious, or organization authorities which has repercussions in the game world. This can result in ostracization, prohibitions, removal of power(s) and/or actions taken to harm or kill the transgressor.
Often times the beliefs have also spelled out a path of Atonement.