The wave of online video coverage this spring and into the summer has missed a critical distinction for advertisers: There is a fundamental difference between TV online and online TV. Knowing it will allow advertisers to build from an assured base online.

I call TV online the 50+ sites where viewers seek out streaming, information and conversation related to their favorite TV shows. I call online TV the compendium of user-, publisher and brand-generated videos that consumers encounter across the Internet. Both get about 20 hours of time every month from U.S. consumers. But they do it in vastly different ways, with real implications for advertisers.

TV online sites grow with viewers’ all-screen appetites. Think ESPN, The Food Network, MTV or SyFy and programs like “The Walking Dead,” “Pretty Little Liars,” “Fargo,” “The Americans” or “Conan.” Their audiences convene predictably because they’re committed to the content, so they form masses with a common source of connection.

Show fans watch wherever, whenever they want; they read about the shows and the talent; they watch companion content (e.g., “Last Chance Kitchen,” the online contest that parallels Bravo’s “Top Chef”); and they share their reactions on-site as well as on social networks. They literally propel the content.

Online TV is a different animal. The portals can be destinations, but the programs don’t have natural audience momentum yet. For every “Gangnam Style” billion-view video, there are thousands of videos and channels gaining viewers but not yet establishing audience momentum. Without regularly scheduled content in common, the audiences are floating and free-forming; they come and go in different directions.

TV online sells pre-assembled mass audiences for predestined showings, primarily through direct sales forces. Advertisers buy known audiences attached to specified content. Advertising appears in video players at the center of sites the audience came for. The models are too simple to game (no viewability issues, no bots/fraud), and there are universally accepted measurements of performance. TV programmers come from a make-or-break heritage: Viewers stay or the model breaks down.

Online TV sells discovered audiences that can be aggregated to mass, primarily through an expanding web of third parties and exchanges. Advertisers buy demographic or behavioral triggers, and impressions are allocated and aggregated algorithmically. Advertising appears in a range of venues, often thumbnail-sized players below the fold.

Importantly, TV online pays programmers enough to keep creating content that’s compelling, consistent and sustainable. It takes a concentration of money and time to create the content that sets up robust advertising environments. TV networks invest enormous sums in original content -- sustainable stories made for serialization -- and audience development. Branded TV programmers put 50% of revenues into owned content (more than $125 billion in the past five years).

In online TV, the biggest portals are just starting to invest millions in original programming. They aren’t destinations for content on a schedule yet, and likely won’t be anytime soon. Online TV pays programmers pennies on the dollar -- the LUMAscape exacts its "tech tax" first -- that don't support continual upgrades in quality.

Advertisers need the right number of customer connections to plan against. For them, the real utility in upfront buying is being able to synch audiences to sales goals, thereby laying the foundation for a year’s worth of relevant audience engagement. Buying right is about getting that foundation with an interconnected audience -- people who propel content (including advertising) across screens.

TV online brings predictability -- planning from an assured base -- into the otherwise uncertain territory of online video. In the process, it forms a hedge against the equal opportunity problem of ad fraud, which can leave an advertiser like Mercedes with a 57% unviewable rate.

Contrary to the rallying cry of some Internet ad titans, it’s not “all video.”

With all advertising, the key is knowing what you’re getting, whom you’re getting it from, whom you’ll attract in the way of audience, and whom they’ll draw in through various forms of social networking. Knowing the difference between TV online and online TV is the first step toward predictable audience momentum that sells more stuff.