Hi, there are no stupid questions, believe me I had a million of them when my Husband was trying to teach me about coin collecting, I am still learning but doing alot better, In the coin collecting field they have tons of abrev for what they want to say? but a RPM is a Repunched Mint Mark, If a date was punched into the die and then punched in again in a different position it is considered to be a repunched date. This is just one of the variety class coins to be collected, Hope this helped, thanks for the question.