Kill multiple processes from terminal

Use pgrep and kill to kill processes in terminal.
For example, to kill all the processes of BetterTouchTool:

# -i to perform case-insensitive match
# kill -<signal> <pid>
pgrep -i bettertouchtool | xargs kill -9

For another example, to kill FaceTimeNotificationCenterService to turn off the camera light left by FaceTime.

pgrep -i FaceTimeNotificationCenterService | xargs kill -9