The most common (and most standard keyboard layout and form) is ANSI — short for the American Standard. There are also ISO and JIS, which are the European and Japanese standards and forms.

If you ever use any of the alternative keyboard layouts available in OS X (System Preferences -> Language & Text, Input Sources tab), you know that some of their names are quite cumbersome—U.S ...

The keyboard layouts appear in the Input Sources tab, and the ones you currently have active will be in the left column. Apple offers several keyboard layouts based on different languages ...