Force quitting an application!
It is less likely than on a PC but it does happen even on a Mac that an application freezes. I used to click and hold on the application icon in the dock to select "Force Quit". It worked well but it really wasn't quick. The other way was to go to the Apple menu, choose "Force Quit..." and a dialog box would pop up with the list of currently running applications. The best is the locked up app would even show up as "Not responding". That was still pretty long and I don't know why but when an app is not responding, it takes a very long time until the Apple menu decides to come up. There is a handy keyboard shortcut that solves everything, however: "Command-Option-Esc". It will instantly bring up the same window than if you go through the Apple menu, but it will take much less time.