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They are different instances of a pseudo terminal. E.g. they are different tabs in a Terminal window.

There is no TTY. This process has detached from the tty. Using the TIOCNOTTY ioctl(), or setsid(). This is traditionally done to become a background process a.k.a. "daemon", which will not automatically be killed by SIGHUP when logging out from a terminal. (If it is a gnome process as in this example, it will likely be expected to terminate by some other mechanism).

Alternatively it may never have had a TTY to start with, as with processes started for a systemd service for example.