Linux – What’s difference between group admin and adm

There is little difference in the command pairs you are wondering about.

The first pair attempts to simulate a fresh login as the new user-- there could be some difference in the environmental variables supplied, as sudo su - is going to try and preserve existing environmental variables, while sudo -i will set very specific environmental variables and strip all others (check your man pages for specifics).

For the second pair, the difference in behavior is this: sudo su will always start the shell listed in the user's /etc/passwd, whereas sudo -s will check the SHELL environmental variable first, and only execute the shell in /etc/passwd if SHELL is unset.

The difference is that xterm is the standard terminal emulator of the X Window System, while gnome-terminal is the standard terminal emulator of the GNOME project.

They are similar because both are terminal emulators.

For more information about why terminals need to be emulated and what a "real" or a "virtual" terminal is read this question and answer: https://askubuntu.com/questions/14284/why-is-a-virtual-terminal-virtual-and-what-why-where-is-the-real-terminal.

A terminal is not a shell. To learn about the difference between a terminal and a shell read this question and answer: https://unix.stackexchange.com/questions/4126/what-is-the-exact-difference-between-a-terminal-a-shell-a-tty-and-a-con.