Ryan Murphy, welcome to the Upside Down.

On Tuesday, the streaming giant Netflix announced that Mr. Murphy — the producer of “Glee” and “American Crime Story” and much, much more — had left 21st Century Fox to join its ranks, in a deal said to be valued at up to $300 million.

That’s a lot of money, but it’s not mine, and ordinarily, I don’t much care how an entertainment Croesus moves around its ducats. TV outlets make big deals all the time.

The reason that this one — like Netflix’s poaching of Shonda Rhimes from ABC last year — has the feeling of a turning point is that, as with all things Netflix, there is a definitional question involved. Netflix, both artistically and as a business, is something different. But what?

Is it most similar to an online-video platform, like YouTube? A network, like NBC? A channel, like HBO? (These questions apply as well to other streamers, like Hulu and Amazon Prime, but to Netflix above all.)