When it was first coined, the noun factoid referred to a piece of inaccurate or unverified information presented as factual. The -oid suffix normally means resembling or having the appearance of, so a factoid is something that has the appearance of fact but is not necessarily factual. The word was coined by Norman Mailer in his biography of Marilyn Monroe, where he defined factoids as “facts which have no existence before appearing in a magazine or newspaper.”
In the United States, however, factoid is now almost exclusively used to mean a brief interesting fact. Elsewhere, the meaning may be in flux, with the influence of American media nudging it toward the newer U.S. definition. This definition is still considered incorrect by people who follow English usage, but it’s so widespread those who dislike it may eventually have to accept it, even if it does contradict the word’s original sense.
Factoid is almost always used in the newer sense—for example:
Here’s an interesting factoid for you: The Mavericks have covered the spread in 15 consecutive games. [Dallas Morning News]
An interesting factoid Mayer mentioned is that more than half of Google Maps usage on the weekends is now on mobile devices … [Forbes]
What’s not rubbish is this factoid: the topic of #RoyalWedding has surpassed 1 million tweets … [Los Angeles Times]
These writers obviously don’t mean to suggest that their factoids merely resemble truth.