What are .CSX C# files for?

I've heard of .cs files but never of .csx files. Google searches led me to CSX corporation and other unwanted bodies. Can someone provide a terse description of what a CSX file is, and perhaps the main differences between CSX and CS?

It is a C# Script File introduced with Roslyn:

C# Script File (.csx) Editing Support: The CTP introduces a concept of a C# Script File. You can create a .csx file [...]

You don't have to have everything in a class and method, a csx file is like it's own method, and everything in the file will be executed on start.

It is a script file used by ScriptCS to allow you to create executables without having to create a project file.

It is Scriptcs file http://scriptcs.net/ . It can executed with scriptcs compiler