Need definition for line of code please?

What is happening here is its taking all the variables in 'files' and putting them through a loop. Each loop iteration it puts the current element of files into 'fn' so 'fn' can be called to do something with it. This is how the new c++ 'for each' loops work. If you want more information look up for each loops in something like c#

fn is not a function, it's a variable that is being used to step thru a collection of strings named files. The code can be thought of as "Get each string from collection files sequentially, naming each occurrence fn and print it out."

fn appears to be a variable

for(int i = 0; i < files.size(); i++)

System.out.println("found " + files.get[i]);