I finally know what the above two words are and how to use them on a Linux machine.
SIGTERM - Send an application a signal to terminate itself the way it normally would, i.e. let it pack its bags like it does. A request to empty its place on RAM.
SIGKILL - Just kill the application. No bullshit. Shoot it with the sniper. No confusions.
How to use them:
You need to find the process id for of the app you want to kill -15 or kill -9, i.e. terminate or kill, respectively.
to find the pid (you can just type part of the app's name here):
or, if you know the exact console name of the app:
Then, kill that app
kill -9 pid
Or, politely ask it to terminate
kill -15 pid