OBJ - A fake character that takes the place of a real object, like

A fake character that takes the place of a real object, like when you use a stick instead of a sword because you're too lazy to find one.

This OBJ is just a broom I found in the hallway.

I used a banana as my OBJ because I ran out of snacks.

The OBJ is just my little brother pretending to be a dragon.