pkill is a program that can be used to send a signal to a processes, by specifying a regex pattern that matches part of the process name (or it’s full command line name with the -f option).
The most direct way to kill a process is with:
$ sudo pkill -9 "this_matches_part_of_process_name"
-9 option tells pkill to issue the SIGKILL signal.
pkill can be the nuclear bomb of all kill tools, as it is surprisingly easy to make the pattern too weak, and it matches something you didn’t intend. And a way to crash your computer:
$ sudo pkill -9 ".*"