Hi All,
Today I will be discussing the type of files used in Symbian.
My intention is to provide a handbook like structure for definitions of various types of files used in Symbian.
(File means not the usual file system topic but rather the various files used such as rss,hrh,..etc)

List of Files in Symbian
CPP,Header files(.h)
RSS file Resource file.It contains resource definitions for UI related things like menu, dailogs etc. On compilation 2 files are generated (rsg & rsc)
RSG file It is a header specifying resource identifier. To be included by the cpp files for UI identifiers.It will be present in \epoc32\include
RSC file The binary code for the rss file.(Object code)

BMP file Image file format.Used commonly across all platforms.
MBM file Symbian bitmap files. Symbian understands MBM format. Multiple bitmap files can be embedded within one BMP.
MBG file Its a dynamically created header-file used by the application. (same like RSG concept). To be included by the cpp or rss file if bitmap images are used.

HRH file Enum declarations that are used in resource files,cpp and the normal header files are done here.

LOC file Used for localization.Strings which are used in rss file should be #defined in LOC files if your applications needs to support variety of language.
RLS file Same as loc files. Only difference is the syntax used. Instead of #define we use rls_string id.

MMP file Make file. Used to specify header file locations, source code to be compiled, library to be linked, UID value assignment etc

DEF file It's used for libraries (dll). The file contains the mapping of exported function to a ordinal number.abld freeze generates def file. It's used for BC (backward compatibility)

IBY file contains files which needs to be placed in the mobile(The destination path is mentioned along with the source path in the work space)

My team mate Jagamohan has reviewed this topic and I thank him for corrections.