Marissa Mayer (Photo credit: jdlasica)

Cross-posted from my Forbes.com blog The New Persuaders:

Everybody has all kinds of advice for Yahoo’s new CEO, Marissa Mayer. Hire great engineers. (Well, duh, but how? Big money alone won’t do it.)  Fire 10,000 people. (Sure, Marc, easy peasy–that should help with recruiting too.) Fix Flickr. (Right, and 47 other services while you’re at it.) Go mobile. (Years late, that should work.)

Granted, most of those things may well be necessary at some point, and probably soon. But here’s what everyone from employees and advertisers to users and investors needs to know first: What is Yahoo?

It’s a question that has produced unconvincing answers for so many years it’s hard to remember by now what made Yahoo unique. Yahoo itself takes a direct crack at it on its “Investors FAQs” page, answering the very same question, “What is Yahoo!?”:

“Today, Yahoo! Inc. has become the world’s largest global online network of integrated services with more than 500 million users worldwide.”

Ugh. “Digital media company”? Makes my heart, uh, flatline.

It also has an actual “mission or vision statement,” a clear carryover from Carol Bartz, two CEOs ago:

“Yahoo! is the premier digital media company. Yahoo! creates deeply personal digital experiences that keep more than half a billion people connected to what matters most to them, across devices and around the globe. That’s how we deliver your world, your way. And Yahoo!’s unique combination of Science + Art + Scale connects advertisers to the consumers who build their businesses.”

A little better, but really, “Science + Art + Scale”? Hard to imagine that means much to advertisers, let alone consumers. (I was always surprised Bartz didn’t call it Art + Science + Scale to provide a more characteristically salty acronym.)

Still, there’s a kernel of something in the part about keeping people connected to what matters to them. I will hazard an unpopular view that Yahoo’s original mission as a portal still has fundamental appeal to many people. Most digerati will say the portal is dead, and good riddance, as people flock to more focused services such as Facebook’s social network and Google’s search engine. So if Yahoo comes out and says it’s a portal, it will become even more of a laughingstock in the tech community.

But even Google and Facebook increasingly are becoming hubs for all kinds of activities, even if they will never utter the P word. So it seems clear that a very large number of people out there want someone else to help them decide the best services and apps to use online–and provide a way for them to work together and share data in ways that are useful to us, not just advertisers. It’s also clear that many people are leery, thanks to privacy concerns or simply because they may miss the latest and greatest from that new upstart, about going all-in on Google or Facebook or even Apple.

At its heart, Yahoo’s value, when it has had value, is providing people easy, curated access to the best online services out there, whether they’re Yahoo’s own or others’. That’s a media company, however that’s evolving today and will continue to evolve in the future.

Of course, a vision only works if you act on it, so ultimately, what will really matter is creating new services people can’t live without. Those are now few and far between at Yahoo, though a few like Sports and Finance come pretty close. Spurring the creation and execution of new ones is where Mayer could shine where her predecessors did not.

But Mayer’s vision needs to acknowledge that Yahoo’s future can’t simply rest on pumping out cool products. It needs to be more meta than that in an era when only a couple behemoths can even think about providing everything on their own (and even Google has throttled back its habit of throwing stuff against the wall to see what sticks). And dozens of smaller companies are providing best-of-breed services that Yahoo will be hard-pressed to compete with.

The way Yahoo becomes a 21st century media company, a concierge of online services, needs to be fundamentally redesigned for the mobile era, of course. I still use MyYahoo a lot because I’ve populated it with stock lists, key news sources, access to email accounts, quick views into other services such as Twitter and Facebook, and more. But the desktop version is a fright on my mobile phone, and the mobile version is simply a long list of seemingly random feeds.

Yahoo, of all companies–the one that famously kept its home page simple enough early on that it wouldn’t take more than a few seconds to load on slow dial-up connections–should be able to figure this out. Even Apple, with the random scattering of apps across multiple pages on its iPhone, hasn’t figured it out. But I’d love to see it, and I and a few hundred million other people wouldn’t mind getting it from Yahoo.

For her part, Mayer provided a provisional vision of what Yahoo is or should be to the New York Times: “My focus at Google has been to deliver great end-user experiences, to delight and inspire our end users. That is what I plan to do at Yahoo, give the end user something valuable and delightful that makes them want to come to Yahoo every day.”

But that “something” is far too diffuse, and surely she knows that. As a former product chief at Google, Mayer may face a challenge doing the vision thing. She needs an elevator pitch, yes, but more than that: She must make a clear, bold statement of why we should continue to type Y-a-h-o-o into our browsers, or install Yahoo apps on our smartphones.