Possibly the worst Harry Potter couple made in the history of fanfiction. HP/RW is short for Harry Potter / Ron Weasley. This is put in the story's summary to indicate that the characters come into a romantic situation together. Authors often use the excuse that these two characters "are such good friends that they should end up together". What ever tickles your fancy, I say.
Story Summary Example:
"Those Green Eyes": Young Ronald Weasley has wanted something his whole life, and finally this summer vacation he is going to get it. It all starts when Harry comes for a late night visit...HP/RW