Windows resource script
From Just Solve the File Format Problem
A Windows resource script (also called a resource file, and other similar names) is a text-based file used to define resources used in the development of Microsoft Windows software. Such files are used mainly with traditional "Win32"-style software, and not necessarily with other frameworks such as .NET.
Although resource scripts can be written manually, a specialized resource editor is usually used instead. Unfortunately, the free editions of Microsoft's development tools often do not include a resource editor.
A resource script is typically compiled to a (Windows resource) (.res) file, and then linked into an EXE or DLL file.