Chrome web apps aren't new, the Web Store is several years old now. But, while plenty of great web apps have been created in that time, even more are just plain websites packaged as an app. All these do is add a shortcut to the website in the new tab page.
"True" web apps for Chrome work offline and offer some extended functionality, but not much beyond what would be possible on the web or to a Chrome extension.
There is a "next-generation" category of Chrome web apps, called "packaged apps," coming, though, and these can be considered truly on par with native apps.
Google has been working on supporting these new apps, by creating the new APIs in the first place, for a while now, it first mentioned them during Google I/O, last summer.
Now, it has taken a major step by expanding the Chrome OS app launcher to the desktop platforms, starting with Windows.
The app launcher for the desktop has been in testing for months, but users had to enable the feature in chrome://flags. It's now enabled by default.
If you install any of these packaged apps from the Chrome Web Store, you'll have the option of adding the app launcher to the Windows dock.
You'll then be able to launch any of your current Chrome apps, which will open in a new tab in Chrome, but also the new packaged apps which open in their own window.
Packaged apps use their own UI and even their own window, you don't need to have Chrome open to use them, though, technically, Chrome would still be running in the background.
Apart from that major distinction, packaged apps will also be able to "do" more than regular web apps. The idea is to make it possible to replace most if not all native apps with Chrome packaged apps which are easy to find and install.
While these apps are great on the desktop, they're crucial for Chrome OS which doesn't have any support for native apps outside of Chrome itself.
Packaged apps should be supported across platforms by default in the next few months, possibly ahead of the touchscreen Chromebook launch.