The word “thing” has, of course, long played a versatile and generic role in our language, referring both to physical objects and abstract matters. “The thing is …” “Here’s the thing.” “The play’s the thing.” In these examples, “thing” denotes the matter at hand and functions as stage setting to emphasize an important point. One new thing about “a thing,” then, is the typical use of the indefinite article “a” to precede it. We talk about a thing because we are engaged in cataloging. The question is whether something counts as a thing. “A thing” is not just stage setting. Information is conveyed.
What information? One definition of “a thing” that suggests itself right away is “cultural phenomenon.” A new app, an item of celebrity gossip, the practices of a subculture. It seems likely that “a thing” comes from the phrase the coolest/newest/latest thing. But now, in a society where everything, even the past, is new — “new thing” verges on the redundant. If they weren’t new they wouldn’t be things.
Alexander Stern, “So, Is That a Thing?”, The New York Times (17 April 2016), SR9.