"Reference" has a very particular meaning in C++. It's not interchangable with the word "variable". I don't know whether you used the word "reference" as opposed to "variable" intentionally or not or if your question merely concerns the word "static". Here's a link on "reference".
"Static" means a couple of things, depending on how you use it. Thus the line you provided would have a different meaning depending on the context it's used in. Basically you have "static" as used with classes and "static" as used when you're not dealing with classes. You use them often for different purposes depending on whether you're using a class or not.
Do you know what a global variable is ?
Do you know what a local variable is ?
If so then read on.
Static variable is a mix between the two. Static variable has the same
lifetime as global, while its scope could be contained like a local variable.
Re-read William's classic total example, while thinking about the