The privacy of the crowd. Someone sitting on the stoop watching people go by is just a people watcher. If he starts following you around ducking around a corner when you look back, he's a stalker.
If he starts making records of everywhere you go, your route there, how long you remain and what purchases you make and who with he is a corporation violating your privacy.
You see in public you don't have an expectation to not be seen. You do have an expectation that you won't be tracked, or at least you used to have before the corporate espionage state took over.