Q:

Is there a way a website can accurately determine the source domain that reached it?

I have a website where I click on a link and am redirected to another website.
Is there a way, the other website (www.otherwebsite.com) can determine accurately that the request has been sent from my website www.mywebsite.com?

A:

Yes, using the HTTP header called "Referer" (no, that is not a spelling mistake, that is actually the name of the header).
For instance, in PHP you would do this:
<?php echo "You came from this site: <b>".htmlspecialchars($_SERVER['HTTP_REFERER'])."</b>";

The same code in JavaScript:
document.write("You came from this site: <b>"+document.referrer+"</b>");

This could output:

You came from this site: http://www.mywebsite.com/index.html

