Understand meaning of { when creating stream objects

I came across the following code

#include <iterator>
#include <string>
#include <fstream>
#include <iostream>
#include <vector>
#include <algorithm>

int main() {

    std::string inputfilename, outputfilename;

    std::cin  >> outputfilename;

    std::ofstream outputfile{ outputfilename };

    outputfile << "I exist Yo!";

    return 0;
}

My first reaction was that it should not compile. I had never seen the outputfile{ outputfilename }; usage. Can someone please tell me what feature of the C++ language defines the behavior of {} in this instance?

P.S. The code works and does what you would expect.