Ctags generates an index (or tag) file of language objects found in source files
that allows these items to be quickly and easily located by a text editor or
other utility. A tag signifies a language object for which an index entry is
available (or, alternatively, the index entry created for that object). 

Tag generation is supported for the following languages: 
Assembler, AWK, ASP, BETA, Bourne/Korn/Zsh Shell, C, C++, COBOL, Eiffel,
Fortran, Java, Lisp, Lua, Make, Pascal, Perl, PHP, Python, REXX, Ruby, S-Lang,
Scheme, Tcl, Vim, and YACC.

A list of editors and tools utilizing tag files may be found here:
http://ctags.sourceforge.net/tools.html