OOPArts are out-of-place artefacts, though other objects of historical, archaeological, or palaeontological interest are included. The term was coined by the naturalist and cryptozoologist Ivan T. Sanderson. It isn’t a term used by mainstream scientists as it may be considered tainted with unprofessionalism; it is largely used by those who study the pseudo-scientific topics such as paranormal activities, fringe theories such as ancient astronauts, or the topic of creatures such as Bigfoot and the Loch Ness Monster.
Having said all that, I find it interesting to read about various objects that have been labelled as OOPArt. Here are a few:
The Wolfsegg Iron
The Baghdad Battery
The Dendera Lamps
While some may be explained with scientific methods, other official “scientific” explanations seem to me, frankly, far-fetched. Judge for yourself, and enjoy the curiosities of our planet’s history!