What does the dot file icon mean in Visual Studio 2015 Solution Explorer for a .cs file?

Question

What does the icon for this dotted file mean? This is a .cs file, but it does not behave correctly in my project, and I noticed this separate icon in Solution Explorer:

I checked the MSDN Documentation in three places

Another MSDN Page

Another MSDN Page

I also checked the Visual Studio Documentation , which is pretty vaguely organized.

I even checked this site:

Finally, I found this section with a similar question, but the question page and links inside do not have this icon . Thank you for your help.

Answer 1

, . , Show All Files.

" ".

Answer 2

" ".

, .

" ", .

Answer 3

"" , .

"" , " ". , , , , , .

, , , . :

Answer 4

/ .