Yahoo's $1.1 billion purchase of blogging site Tumblr is the biggest move since CEO Marissa Mayer took over the Web company.

STORY HIGHLIGHTS

• Yahoo buying Tumblr is a bid to make its own base younger, cooler
• Founded in 2007, the site hosts 150 million blogs
• Animated GIFs saw a comeback on Tumblr
• There's lots of porn -- an issue Yahoo may have to address

(Doug Gross @ CNN) -- Yahoo's purchase of hot blogging platform Tumblr, which it announced Monday, was big news for the hundreds of millions of folks who already post to the site or check in to follow those who do.

But the $1.1 billion buyout will also no doubt introduce Tumblr to lots of folks not yet wholly familiar with it, even if their Web searches for viral memes and cute kittens have already landed them there unawares.

So, here are some facts you need to know about Tumblr (which, in the grand tradition of Web startups everywhere, shed its "e" early on).

It's big and getting bigger

Founded in 2007, Tumblr has stayed hot on a Web that can be unforgiving once it decides you're yesterday's news.

While its numbers aren't comparable to social-networking giants like Facebook, they're certainly enough to put hundreds of millions more eyeballs on the ads Yahoo serves up as its bread and butter.

Let's face it -- when the White House signs up for an account, you know you're onto something.

To wit (according to the company):

Number of Tumblr blogs: 105 million

Monthly visitors: 300 million

Posts per second: 900

New signups every day: 120,000

It loves an animated GIF

If there was a ground zero for the rebirth of the Web's beloved video loops, it was Tumblr.

Once relegated to the scrap heap of Web culture (we miss you, Peanut Butter Jelly Time), the past couple of years have reminded us of an enduring truth: It's fun to watch a cute duck, a bouncy Olympian or "bros" watching basketball over and over and over again.

Tumblr's quick, visual-friendly publishing platform is perfect for GIFs. Nobody expects a 10,000-word essay. Make us laugh and all is well.

Oh, and how did Yahoo CEO Marissa Mayer choose to make the big announcement? On her own Tumblr. With an animated GIF.

They've figured out mobile

Our society is becoming a mobile one and increasingly, phones and tablets are the preferred portals for people to access the Web.

For example, more people now access Facebook via mobile than on the traditional Web (a fact the site has had to aggressively address to stay relevant and make stockholders happy).

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But while some desktop titans are having to adjust, Tumblr is already living comfortably in that mobile world.

More than half of Tumblr's 300 million users access it with its mobile app, and that crowd does so an average of seven times a day.

There's kind of a lot of porn

Shocker -- there's porn on the Internet.

But while most any corner of the Web that allows user posts is bound to have its share of naughty bits, Tumblr has become a go-to spot for adult-entertainment industry types and amateur smut-lovers alike. (The company, of course, doesn't say what percentage of its site is adult content, but a recent analysis puts it at over 11 percent.)

And the site doesn't really shy away from that fact, acknowledging as much in its community guidelines.

"Tumblr is home to millions of readers and bloggers from a variety of locations, cultures, and backgrounds with different points of view concerning adult-oriented content," the entry reads, asking users only to make sure to identify such pages as NSFW ("not safe for work") and, of course, not to post anything illegal.

That's all well and good for an edgy startup, but could be an issue that needs to be tackled as Yahoo aims to appeal to as many advertisers as possible.

In the meantime, just make sure you look for those four letters when searching the site.

It's cool

For a few years, nobody's really been sure what Yahoo is, other than a place where an aging user base gets its e-mail and looks at a few news stories.

Tumblr is Mayer's bid to get young and hip -- and it's not a bad bet.

From "Sh*t My Dad Says" to "Reasons My Son Is Crying," the most buzzed-about blogs of the past few years have tended to originate at Tumblr.

Whether its "Kim Jong Il Looking at Things" or "White Men Wearing Google Glass," fun and a little bit edgy isn't hard to find on the site.