Something that doesn’t belong in a given time period. Cavemen eating with knife and fork, for example. Once in a while in Manitoba we have a whole festival of anachronisms, although the word itself is never mentioned. It’s a time where festival goers dress up for the period and often miss a few items, like a camera or a pair of glasses.
I always like to pick out these details. Others dress up completely for the part and don’t get out of character at all.