A ham is an object, person, word, or phrase in media that shows up once and becomes important
later down the
line.
The term comes from the
2019 Invader Zim movie, Enter the Florpus, where a literal ham was introduced into the story and later on was used in the final battle.
"Now pay close attention to that ham,
cuz it's not the last
time you're gonna see that ham in the story." ... "See? There's that ham again."
"God, I had no idea the
cat was gonna be a ham. It makes so much sense now."