SEATTLE—Earlier this year, pictures of a new Windows look and feel leaked. Codenamed Project Neon, the new look builds on Microsoft Design Language 2 (MDL2), the styling currently used in Windows 10, to add elements of translucency and animation. Neon has now been officially announced, and it has an official new name: the Microsoft Fluent Design System.

The awkward MDL2 name exists because the original codename for the geometric, text-centric style introduced with Windows Phone 7 and incrementally iterated ever since was subject of a trademark dispute. That look and feel was internally named Metro, but Microsoft had to stop using the Metro name after pushback from a German supermarket chain. The company didn't initially have any particularly good name to refer to the styling formerly known as Metro, so many people continued to use that term for lack of anything better. It wasn't until a couple of months after dropping "Metro" that a new name, "Microsoft Design Language," was settled on.

Our understanding is that Neon befell a similar fate; someone out there is using the Neon name, forcing Microsoft to pick a different appellation. This time around, however, the company has recognized that it's important to have an official name for the style that it can talk about and describe, giving us "Microsoft Fluent Design System."

The switch from "design language" to "design system" is deliberate; Fluent is intended to define more than just the appearance, but also the interactivity. Though visually there are common elements, the system is designed to work across virtual/augmented reality, phones, tablets, desktop PCs, games consoles, using mice, keyboards, motion controllers, voice, gestures, touch, and pen, with the interactivity and input optimized to each particular form factor.

Fluent is described as having five "fundamentals": light, depth, motion, material, and scale. "Light" means that the interface should avoid distracting and strive to ensure that attention is drawn to where it needs to be. With "depth," Fluent apps will make greater use of layering and the relationships between objects and interface elements. Fluent will use "motion" to indicate relationships and connections between elements, establishing context. Microsoft is using "Material" to mean making best use of the screen space and giving room to content. "Scale" means building interfaces that can go beyond two dimensions, and go beyond the size of a screen, to embrace new form factors and input methods as they arrive.

Aspects of this mirror similar decisions made in other design languages. Google's Material Design, for example, is not a million miles away from Metro/MDL but includes the same emphasis on motion and animation as Fluent now does, for much the same reason: motion can be used to convey context and the relationships between elements on-screen.

One of the biggest issues with Metro was that Microsoft did not provide strong guidance to developers on how to actually build their interfaces. First-party applications are important to any design language, as many developers mine those applications for useful interface concepts and ideas; they serve as the model that inspire third-party application interfaces. The Metro apps that the company shipped tended to all be quite simple, offering little insight into how applications with rich, complex interfaces should be assembled.

This time around, Microsoft is promising to do better. The set of first-party applications using Fluent will be larger, and these applications will have richer interfaces and deeper functionality. This should let them serve as a much better model for third parties to copy and iterate on.

A few apps available to Insider builds of Windows 10 have already started to pick up some Fluent design elements—for example, the Groove music app now sports some transparency effects—and this will continue in the run up to the next major Windows update, the Fall Creators Update. The move to Fluent will not happen within the Fall Creators Update timeframe, however; it's a longer-term project. Microsoft says that even the Creators Update contains some small aspects that were developed as part of Fluent work, and the transition to and adoption of Fluent will take longer than the six-month interval between each Windows release.