In my experience I think of Senior as an autonomous builder of a thing that they are told to build. Staff is the same but may work across multiple teams and he

In my experience I think of Senior as an autonomous builder of a thing that they are told to build. Staff is the same but may work across multiple teams and help define the thing that needs building. They will usually have considerably broad experience. They get thrown at random problems nobody is sure how to fix. Principals extend that concept but may be industry leaders in a field or at least deeply specialised.