I just read a little blurb about "out of place" artifacts. Things that are found (usually in archeology, it seems) in places that it seems quite unlikely they'd be found. You can read more here.
I thought I'd maybe start my own category of OOPart today, as I walked past the beach ball in the hall for the umpteenth time. No idea how it got there, or what it's doing in this rough & industrial random fire exit hallway in the building I work in. But I'm really rather taken with it. And I like the fact that just today I read about OOPart so I have a way to categorize it.