What does cors middleware do?

Was looking at some node js code which created some web API's and came across this:

//CORS Middleware
app.use(function (req, res, next) {
res.header("Access-Control-Allow-Origin", "*");
res.header("Access-Control-Allow-Methods", "GET,HEAD,OPTIONS,POST,PUT");
res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, 
contentType,Content-Type, Accept, Authorization");
next();
});

Have looked around on the internet and can't seem to understand what it does? Can someone please explain the purpose of cors middleware

via user7983422