a. It represents the folder on the file system which contains files that are installed when SharePoint is installed on the Web Front End Server.
b. It is located at the path
C:\Program Files\Common files\Microsoft Shared\Web Server Extensions\15
c. It contains SharePoint binary files, site definitions, feature definitions, page layouts, ULS logs etc.
d. It is also represented by %CommonProgramFiles%\Microsoft Shared\Web Server Extensions\15
e. SharePoint 2013 also maintains a 14 hive for backwards compatibility for SharePoint 2010 customizations
f. All the above