Sending POST data without form

Can i send for example a string or another piece of information to another .php file without it being exposed [thus not by GET but by POST conform to what i know] without using a form?

If you don't want your data to be seen by the user, use a PHP session.

Data in a post request is still accessible (and manipulable) by the user.

Checkout this tutorial on PHP Sessions.

You could use AJAX to send a POST request if you don't want forms.

Using jquery $.post method it is pretty simple:

$.post('/foo.php', { key1: 'value1', key2: 'value2' }, function(result) {
    alert('successfully posted key1=value1&key2=value2 to foo.php');
});