.mod	is a description of the contents of a F95 module emitted by the compiler when compiling a module read by the compiler when compiling a use statement located by the compiler using INCLUDE environmental variable
.obj	is a description of the program suitable for linking
.lib	is an index of the contents of a dll used by the linker
.exp	is an index of the symbols exported by a dll
.exe	is an executable program
.dll	is a dynamic link library located at run time using PATH env variable
.def	is a text file which tells the linker what to put into a .dll