A referral link is one usually includes some sort of user ID so that the referrer (i.e. the person who posted the link) gets some sort of reward, giving them incentive to spam forums such as this. (Which is why they're so frowned upon.)
Okay, now you're making sense! I thought "referral link" meant just that: direct someone to another site. I didn't realize there was an additional layer to it. Thanks!