It is the subject matter behind nearly half of the current top 20 songs in the country, yet it is going mostly unnoticed. In fact, you've already missed it twice since you started reading this article.

So what is it? It is it. And there's no denying it is red-hot in music right now. It is all over the charts:

Beyonce's "Check on It," Chris Brown's "Run It!," the Black Eyed Peas' "Pump It," Dem Franchize Boys' "Lean Wit It, Rock Wit It," Busta Rhymes' "Touch It," Da Back Wudz's "I Don't Like the Look of It," Juelz Santana's "There It Go (The Whistle Song)," the Purple Ribbon All-Stars' "Kryptonite (I'm on It)" ... and it goes on.

It is actually nothing new to music, nor is telling listeners what to do with it.

The Rolling Stones, alone, have addressed it several times -- "It's Only Rock 'n Roll (But I Like It)," "It Must Be Hell" and "It's Not Easy" -- all the while asking us to "Paint It Black," "Let It Bleed" and "Let It Loose."

Hundreds of artists, from the Doors to the Spice Girls to Van Morrison, have demanded that listeners simply "Do It." And who can forget what Devo told us to do to it?

It has clearly got history, but why is it suddenly so ubiquitous?

Dean Jutilla, a spokesperson for eBay, who have plastered it across television screens and billboards in recent months as the center of their latest advertising campaign, has a theory about it.

"I think because it is such a personal thing, and only you can identify with your own it, is probably why so many artists are talking about it," Jutilla said. "It means so many things to so many people"

And Jutilla has a point. In an attempt to find out exactly what it is, MTV News asked a variety of it experts and got, well, a variety of answers.

"It's basically something really unique about you and having some star potential," said "American Idol" judge Randy Jackson, who is always talking about singers having it or not having it. "It's the thing that Elvis had, the thing that Michael Jackson had, the thing that so many greats have. When you walk into the room and you leave, everyone remembers you or people are saying, 'God, I like that person,' or 'I want to be like that person,' or 'I want to dress like them,' or 'I want to sing like them,' just having some kind of inspirational, motivational factor about you."

Of course Jackson is more of a pop and rock guy, and it seems to be more prevalent in hip-hop and R&B, so we went to expert rap author Kris Ex, who most recently penned 50 Cent's biography.

"If you gotta ask, you ain't got it, ain't getting' it and can't touch it, much less pump it or check on it," Ex declared. "It is what it is and that's all that it is. That's all there is to it, really. Well, there may be more, but I'm not at liberty to talk about it. It's like a secret society -- or something."

Yesi Ortiz, a DJ at Los Angeles hip-hop station Power 106, certainly doesn't need to ask.

"Come on, everyone knows that it is the secret code word for Jennifer Lopez's [most famous asset]," she said.

J. Lo aside, Ortiz probably has the most accurate definition of it as it is used in many of today's popular songs, but you never know. And that is basically the whole point of it.

"It is such a personal thing for people," Jutilla reiterated. "And they're very, very protective of their it. No matter what it is to them. They'll even be feisty protecting their it. They are very fascinated and intrigued by it. They'll spend a lot of money on it, whatever that is. I think people find their it empowers them. It brings people together."

Last year, actor Crispin Glover dared to direct a movie called "What Is It?," but when we reached out to him to ask what it is, he simply replied, "The question is not 'What it is,' but what is it?"

So where does that leave us? Perhaps we're best left turning to former Faith No More singer Mike Patton, who asked and then answered "What is it?" it in that band's biggest hit, "Epic": "It's it."

Or maybe we should listen to the Beatles and simply "Let It Be."