Exit the Terminal Window

It is best to let an operation in the terminal finish.
But, if you have a reason to stop it, then the best way to stop is by pressing CTRL + C [Control C] on your keyboad.

Whatever it is safe to close with the X button depends on the process or operation itself.

Just remember the Ctrl + C command ;-)

To exit from terminal is better to type:

exit

or to press the keyboard key

ctrl+d

So you will be sure all pending/running software bind with your terminal session are ended...

both typing exit and hitting <Ctrl>d seem to work in an empty terminal session, but if I hit <Ctrl>z after a man command, now I get something similar to what I thought I had when I originally opened this question:

ubuntu@ubuntu:~$ man gksu

[1]+ Stopped man gksu
ubuntu@ubuntu:~$ exit
exit
There are stopped jobs.
ubuntu@ubuntu:~$

If it type fg, then I can exit.

But sometimes, I needed to hit q to properly exit the man page scroller.