Kinktionary
More like guidelines and a lot less like definitions.
Power Exchange
The assigning of power or control over one person to another (or others). This is consensual and sometimes seen as a 'gift' from the person giving up their power e.g. from a submissive partner to a dominant partner.
24/7 Power Exchange
This is a dynamic where power exchange is always or nearly always present in some form between people during their daily lives. This is often seen between master and slave dynamics.
Authority Transfer
Within Core BDSM Authority Transfer or Power Exchange has a different meaning to the terms used by the kink community.
An authority transfer is where a slave or submissive irrevocably transfers all of their agency to their Dominant or Master. Consent is still given to the AT but consent is not renegotiated for each activity.
In a Total authority Transfer or Total Power Exchange in Core BDSM there are no areas where the submissive (slave) retains their agency, or such areas are so irrelevant not to count. The slave is considered to be the property of their Dominant who assumes the title of Master. This process is consensual and has nothing to do with historical slavery. Once consent to the TAT is given, withdrawing consent will break the dynamic, similar to ending a marriage.