Norman Mailer made this word up to describe the plausible, but not necessarily true, bits of information about a product.
Generally factoids come with the goal of selling a product. The word ‘factoid’ has come into common usage and is a popular term. The definition of factoid might, itself, fit the criteria of being a factoid.
The Oxford English Dictionary tells us:
A. n. Something that becomes accepted as a fact, although it is not (or may not be) true; spec. an assumption or speculation reported and repeated so often that it is popularly considered true; a simulated or imagined fact.
B. adj. Of or having the character of a factoid, quasi-factual; spec. designating writing (esp. journalism) which contains a mixture of fact and supposition or invention presented as accepted fact.
Check out the etymology here.