in UNIX/Linux all processes communicate to each other using system of so-called signals. Some signals are traceable, it means that a process can catch the signal and respond (or react) and not-traceable (that go directly to process structure and remove the process). "kill" is the command of user level that sends the signal. you can see the list of available signal by "kill -l". "kill -9" will send "TERMINATION" signal to a process, means kill it, but it is only one of 15 signals. My advice, get Evi Nemeth book http://www.amazon.com/Linux-Administ...6866800&sr=8-1
or "Learn Linux" DVDs by UNIX Academy http://www.amazon.com/gp/search/ref=...47&rnid=491286
they explain these subjects very well.
Many daemons know how catch specific signal, and let say re-read their configuration file (kill -1 is popular)
hope it helps