Microsoft has laid down its guidelines for the naming of Windows 10 apps, although it's likely that confusion will still reign.
While Microsoft is selling Windows 10 on the concept that everything "Windows" branded will work across every possible Windows platform, from Windows Phone through Xbox One all the way up to desktop Windows, the reality is a little different if you're an app developer, because the different hardware infrastructures means that not every single app will in fact be absolutely universal across those platforms. New Windows 10 apps should be universal, but there will be apps, especially legacy ones, that only run on the desktop version of Windows 10.
It's a tricky and somewhat subtle issue to get across, and Microsoft's plans for how it will refer to the two different app types probably won't help all that much. Speaking at Microsoft's WinHEC developer event, Microsoft's Don Box stated that while it has referred to apps as "universal" in the past, this isn't how Microsoft actually refers to them. "Sometimes we say universal apps, but we call them Windows apps."
So what's the difference? According to Box: "Windows apps runs on all devices, Windows desktop app is PC only. Windows apps run everywhere."
So if it has Desktop after the name, presuming the developer follows Microsoft's lead, it's a desktop/laptop product only. Otherwise, in theory, it will run on everything. This seems fraught with potential confusion if developers aren't crystal clear in their app descriptions, but I guess we'll find out when Windows 10 ships later this year.