Rum Ham originated in Season 7 Episode 2, The Gang Goes to the Jersey Shore. Frank brought the ham so that he could get drunk while eating on the beach, leading to a Cast Away-esque series of events.
The ham appears to be a normal ham soaked in rum, as well as having two pineapple rings for eyes and a red cherry for a nose, again continuing the 'Wilson' in Cast Away themes.
The ham has reappeared in multiple episodes, such as Season 10 Episode 6, The Gang Misses the Boat, and Season 11 Episode 2, Frank Falls Out the Window.
The ham has gained a significant cult following, with multiple people recreating the famed ham on cooking websites, as well as fanfiction pieces of art being drawn of the ham.