Ctrl is the Control key.
Alt is the Alt key.
Del is the delete key. (For Mac users who don't have a backspace key, it's the one under the help key, or below the F13-15 keys).
Control Alt Delete was created by Microsoft to make sure that you weren't sending your user name and password to a website. It was also created to fix crashed applications and force-reboot your computer. They had to do this, probably, because nothing worked.
Ctrl-Alt-Del can never be used by a website to enter your password, exactly Microsoft's point. If you send your password to another website, they can eventually hack into your computer and delete/add/make virus files. Not good.
Fortunately for Mac
users, Ctrl-Alt-Delete is not required, mainly because 1. There are two Delete keys, and 2. There is no alt key. (Actually, there is an alt key, but it is in the option key too, so technically it is not the Alt key.) Also, the Macintosh is almost imposible to hack thanks to its Unix structure and secure operating system