Library folder

Library is the name of several folders on a Macintosh running Mac OS X. It is typical to see several Library folders on a Mac running OS X.

Library folder on root of hard drive
The Library folder on the root level of the Mac OS X startup volume contains application and system files which are used on a systemwide basis.

Library folder in System folder
The Library folder in the System folder contains everything inside the System folder.

Library folder in home folder
Inside the home folder of every user is a Library folder which contains items available only to that user.