When, for example, someone sends you a link to a product listing on a website, you'll get to view it in that retailer's app - even if you don't already have it installed on your phone or tablet. Android will load only the relevant parts of the app on your device, on the fly, which means there won't be a lot of waiting to do while that happens.
And if you're happy with the app and want to actually install it, you'll get a button for that too - just tap on it and the app will be on your device.
Android Instant Apps will be supported on OS versions going back all the way to Jelly Bean, so this functionality will be accessible to over a billion users. The new feature will be out for consumers to play with "later this year", Google says. In the meantime, developers can start working on making their apps compatible.
For now, Google has partnered with a small number companies to "help refine the experience", including BuzzFeed, B&H Photo, Medium, Hotel Tonight, Zumper, and Disney.