I don't have a definition, I just use the thing. That's why I'm asking, I'm not a computer scientist. Eg:

    $f = function helloAction(Http\Request $request) {
        $response = new Http\Response("Hello " . $request->query->get('name'), 200);
        $response->setMa // at this point the IDE will show a list of methods like 'setMaxAge($time)', because it knows its type
    };

Now I can pass $f somewhere else, like this:

    $someObject->someMethod($f);

And the method can accept it like this:

    protected method someMethod($f) {} // no checks!

Or like this:

    protected method someMethod(\Closure $f) {} // only an argument of type Closure will be accepted.

So those are types for me. If you are asking for something like this:

    Response $r = new Response(...);

Then yeah, PHP doesn't have that. Though I don't know why we would want that, it's kind of redundant.