I've noticed during SpaceX streams (this could happen with other LSPs but I've only noticed it with SpaceX) that shortly after the vehicle goes to internal power the controller says "Vehicle is in self align". What exactly does this mean? My best guess is it has to do with the flight computer being ready for launch but not 100% certain.
Up until that point in time, ground control has been regularly telling the vehicle where it is in inertial space relative to the center of the Earth, and in which direction it is pointing in inertial space. "Vehicle is in self align(ment)" represents a mode change where the launch vehicle's flight software begins to use the vehicle's onboard navigation sensors (gyroscopes, accelerometers, GPS, and later, star trackers) to navigate itself. The vehicle begins to be on its own.