PID review

What's a process?
every process has a unique ID: Process ID
Use ps -ef and ps waux to get PIDs
pstree shows a lineage of processes
kill [PID] is the command to terminate a process
What's the difference between kill -9 and kill -15?
kill -1 PID:
How do we get more processes?
What's a daemon?
There should be no hidden processes in Linux