Need Help! Coupons!

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Ok, I have found many sites that allow you to print coupons but I keep finding these things that say use the 3/8RP for an additional $1 off savings or something like that. What is a 3/8RP? Can anyone help me please? I feel dumb but for the life of me I can't figure out what they are talking about. There are several different codes like another one I wrote down is 4/26RP and some are like 5/P. Please explaine this if you can.