The empowered and higher order deity/entity/patron or animus that the Follower is bonded/dedicated to through the Rite of Dedicated Grace. This is regarded as the wellspring and incarnation of the Tenets and actively works toward them through the worship/veneration of followers using Shared Litany and Abiding Litany. These type beings exist out of time for the most part. The bond with the Principal acts as a Higher Order being that is the interface point to The Pattern in terms of perception of objective reality.
Generally a character can only possess the benefits of a single Major (elevated above all others), and a number of Minor Principals equal to their Divine Aptitude or Synergy Pool/10 (or a minimum of 1; whichever is greatest). Each entity has its own set of Prime/Principal Pools tied to it. These are measures that ties a Follower to a specific Principal. The measures is granted by and can only be recognized by that specific Principal. Some measures may only be used in service to the Principal they are associated with, depending on the Follower status of the one possessing the pools.
An Aspect is a label that represents an ideal, manifestation, type, or kind of place or force in the Multiverse. All Principals and most Prime Entities represent or are associated with one or more Aspects. This relationship between entity and aspect defines the types of powers the entity is able to control and to a certain extent, pass on to Followers. Aspects are not [generally] explicitly unique to Principles. Each entity has many orders, cults, and institutions which each focus on different aspects of the deity in the life of followers and the world at large. Ex: One Aspect of Thor is thunder.
Principals do not have to have a defined domain that they represent. They may be known for, and have extra powers with one type of power, but in general reflect a collective Aspect. This is where a group of Prime Entities are part of a compact and together, collectively represent a set of aspects or ideals. This is typically a Unified Pantheon.