Permissions are actually expressions made up of resources, actions, and rules, but for the purposes of this discussion, we will only consider the action -- the aPriori operations that can be permitted or denied by Access Control:

These are mostly self-explanatory except for Cost Using. This permission action applies only to VPEs and determines whether you can cost a component against a particular VPE. There is also another advanced permission called "Associate" which administrators use with Permissions and Groups.