Must be the 'ref' in the URL: http://www.amazon.com/Winco-SPF6-6-Inch-Pan-Full/dp/B001VZ6XP4/ref=sr_1_2?s=kitchen&ie=UTF8&qid=1415225609&sr=1-2&keywords=steam+pan

In this case, I think it stands for 'reference' as opposed to 'referral'. Referral links are in this format: http://www.amazon.com/dp/[code]/?tag=[referral user id]