What does an orange square by folder in Package Explorer mean?

I'm completely new to Java and Eclipse. I developed my first "Hello, world" program the other day following along with a tutorial. I understand most of the Eclipse UI since I worked with Flash Builder for awhile which was built on top of the Eclipse IDE.

My question is, what does an orange square by folder in Package Explorer mean exactly? I imported the project "Hello, world" into the workspace on OSX and that's the first time I ever seen this orange square. I am really curious about it as it isn't on any of the rest of my projects?

I referred to; http://help.eclipse.org/kepler/index.jsp?topic=/org.eclipse.jdt.doc.user/reference/ref-icons.htm

For a reference of icons in the Kepler IDE (btw that's what I'm using) and I found an orange square amongst the icons labeled "a monitor that is owned by a thread"; I don't understand the termonology used though... I don't even know if that is the correct icon I'm looking for?

Here it is;

And here's a screenshot of my package explorer...

See them orange-looking squares? They look very similar but I'm not 100% sure. I really appreciate your help on this.

Thank you!

That's not quite an orange square; it's an orange hard-disk symbol. It indicates that the file or directory labeled is under version control. (A plus in that position indicates that a file has been added to the git index but not yet committed, and a question mark indicates a file that is not under version control when its containing project is.)