Three Different Library Folders
Mac OS X has three different Library folders located under the Macintosh HD:

• /System/Library
• /Library
• /Users/<short name of user>/Library

/System/Library Folder
The /System/Library holds files that OS X needs to operate and function.  These are some files tied to the operation an inner workings of the Mac OS X operating system.  You shouldn't modify the contents of this folder.


/Library Folder
The /Library folder contains files available to ALL users and applications running on OS X.  These are shared and common files.  For example, fonts and printer settings.  This folder can be modified by the Administrative user.  This is the folder where third-party software and applications place the support files that they need to operate.

User Library Folders
The /Users/<short name of user> folder is user specific and holds files and settings as they relate to a user's  individual's preferences, recent items, web site bookmarks, Address Book entries, keychain, Widgets, and so on.