Resource credits are like bandwidth. It was reprogrammed and named in HF20 to try to curb abuse of SPAM accounts.
Basically, it is a fancy way to limit how much people can spam on the blockchain in comparison to their SteemPower.
To stop accounts with 0 stake from being able to generate tons of transactions.
As a side effect it also stops some real users from being able to transact as well.
I thank you for the information! If Jeremy has problems with bandwidth, I'll give him some of my SP as necessary. Since his written articles are so long at times, I am concerned he might run into the old bandwidth problems I had. @hilarski had to step in to help a brother out to get me up and rolling. Thanks again, Randy! I'll never forget how you helped me so much in the beginning.