Senior at a lot of the larger companies I've interacted with is often a kind of a "terminal level", meaning that you're not expected to rise above it, and can comfortably spend most of your career at that level.

Staff, sr staff, principle and other monikers are usually about affecting change at the scale larger than your team, operating at larger scope, and growing people around you.

Senior would be someone who takes the lead on projects in their domain across their team/other teams. Principal would be responsible for leading overall architecture for multiple teams/departments or a super expert in some domain. At Google, probably less than 1% will reach principle, I've heard around 25% of engineers are senior+.