BOB GARFIELD:  There it sits on a Facebook fan page or on some third-party site, like the Huffington Post, adjacent to some content you've just consumed. Ohh, it's a blue thumb sticking out like a hitchhiker's in the cold. It's the "Like" button.

   [MUSIC UP AND UNDER]

You're in a hurry but what the hell. Slow down and click it.

  [TITO NIEVES: I LIKE IT LIKE THAT/UP & UNDER]

Ninety-three percent of Facebook users like it like that at least once a month. Here's what happens next:  If you've liked something within Facebook itself, you send a thumbs up back to your friend on her page. If the button was embedded next to content outside of Facebook, you've just shared the item with your friends, near-friends, family and vague business acquaintances on your own wall and possibly their news feeds.

And if you've liked something posted by a brand, such as Coca-Cola, you may be hearing from Coke with more opportunities to, as they say in the social media marketing racket, "engage."

Jason Kincaid writes for the website TechCrunch.

JASON KINCAID:  Many people may not realize when you hit that "Like" button next to a, a brands icon, whether you're browsing the Web or if you're viewing their Facebook page, you're basically saying like, hey send me stuff.

MICHAEL DONNELLY:  If we were to put a post out there to ask a simple question as to if you were to share a Coke today with someone famous, who would it be?

BOB GARFIELD:  Michael Donnelly is director of worldwide interactive marketing for Coca-Cola.

MICHAEL DONNELLY:  We might get upwards of 20,000 pieces of engagement to a simple post like that. And generally, 90 percent of them are within the first few minutes, or at least within the first hour.

BROOKE GLADSTONE:  Twenty thousand seems huge, until you remember that Coca-Cola has been liked or before the "Like" button “fanned” 57 million times, which is not just a fan club, it's Poland. But why do we "Like?" The first reason has to do with what psychologists call self-presentation or badging. It's why smokers choose Marlboro over Kent or why you read People Magazine in the bathroom and The New York Review of Books on the subway. It's a means of projecting yourself as you wish to be understood. The second reason for “liking,” says Sam Gosling, a professor of psychology at the University of Texas, is simply that it's, well, friend-ly.

SAM GOSLING:  It's equivalent to, you know, when a group of people meet and they start cooing to each other, “Oh, I like your shoes, oh yeah, your hair's so nice now, you've cut your fringe."

BOB GARFIELD:  Simple friendliness, he says, is actually beyond simplicity. It is literally primitive, as in primates.

SAM GOSLING:  What they're doing when they're grooming each other as they're, you know, picking the fleas or whatever out of one another's coats, and they're doing it in a public way, with "we are connected" and "others can see we are connected" and "we are friends, right?"

BOB GARFIELD:  And all those public acts of friendship, the grooming and the sharing and the compromising photo tagging are largely why Facebook is now worth an estimated 100 billion bucks. The "Like" content keeps users on the site longer for advertisers to reach them and produces scads of details about you for better targeting of ads. The "Like" button is so important, in fact, that it has been studied like the Dead Sea Scrolls. A recent white paper from an Indianapolis consultancy called, tellingly, ExactTarget, found that users under 34 are far more likely to like a brand, that 58 percent of people who do like brands are hoping to be rewarded with discounts or freebies. Oddly, what ExactTarget hasn’t been able to target, exactly, is what dollar amount a "Like" is worth to a marketer, compared to say the cost of advertising. All anyone knows is:

K.D. PAINE:  There's a valuable type of "Like" and there's a less valuable type of "Like."

BOB GARFIELD:  That's K.D. Paine, a New Hampshire research and marketing consultant who spends her days and nights imagining measurement standards comparable to the Nielsen TV ratings that worked so well in the mass media good old days. Engagement may be the goal but you can't count it.

K.D. PAINE:  I'm part of five committees, I think, trying to set standards for social media measurement, and all of those standards that are being driven by the need on the part of the advertisers to put real numbers around this thing called social media, this thing called the "Like."

BOB GARFIELD:  This priceless, in every sense, thing called "Like." Complicating calculations is a Facebook algorithm called EdgeRank, which sorts through all your incoming, from your cousin, your best friend, that guy what's-his-name who used to work in Accounting and the Coca-Cola Company. EdgeRank weighs your closeness to the source, the nature of what's being shared and how long ago it was posted, and whatever makes it through EdgeRank's filter winds up in your newsfeed. Everything else does not. So if Coke posts something that EdgeRank ranks lower than a lot of people's cousin's bridal shower photos, says TechCrunch's Jason Kincaid:

JASON KINCAID:  Then the users simply won't see it in their newsfeed at all. And so, it's almost as if Coke doesn't have that fan in the first place.

BOB GARFIELD:  Yeah, don't lose any sleep fretting over Coke's visibility. The population of virtual Poland keeps very busy posting Coke photos and Coke stories and Coke videos, such as this one reenacting a pilgrimage to Coca-Cola's Atlanta headquarters from the fans who started the Coke Facebook page back in 2008.

  [CLIP/MUSIC UP AND UNDER]:

SPOKESMAN:  Welcome to Coca-Cola.

BOB GARFIELD:  Marketing exec Michael Donnelly.

MICHAEL DONNELLY:  Something that astonishes me every day is the great length that people go to, to create things that are somehow relevant or very centric to this brand.

BOB GARFIELD:  And why? Because [LAUGHS] they really like Coke and they really, really like "Liking." Because "Liking" isn't just innate in the primal flea-picking sense, it's like “liking” with a lower case "l." What's not to like?

   [SOUND OF LIKE ADLER AND SISTER LAUGHING/TALKING]

This baby likes watching her big sister. She's the daughter of an Israeli couple, Lior and Vardit Adler. In honor of their favorite Facebook function, they named their daughter - Like.

     [LIKE/SINGING UP AND UNDER]