kill
ProcessesPackage: procps
Sends a signal to a PID: TERM by default, which asks the process to stop, KILL which asks nothing. The -9 in this site's name is the second: it lets the process neither close its files nor write anything.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
kill -l- Lists the existing signals with their numbers, on the machine you are on — the numbering is architecture-dependent.
kill -s- Names the signal instead of numbering it:
kill -s TERMreads back,kill -15has to be recalled.