Microsoft's fluent design is a mix of android's material design and iOS blurred UI

Windows is all set to get a major overhaul to its UI with the upcoming fall update.All the buzz is about Fluent design (previously called project neon) its basically updates current design of elements which is very flat and opaque and adds a depth and transparency to it..

Here is a video showing five key elements that would be like guidelines for the developers to make their apps on

There are five elements that will build the whole UI and framework of the apps and the OS itself. to summarize :

Light
Adds a pointer to elements just below the cursor / pointer. It also illuminates elements on which the focus is. this will be used widely in hololens and surface pen interface rather than a mouse interface.

Depth
Adds shadow elements which creates a depth and parallax effect. which is similar to material design in android. This will also change depth depending on apps and with correct animations, it can look a lot less boring as compared to current flat design.

Motion
Adds and enhances current animations to be more fluid and helps to add transitions between tabs, pages, windows, menus etc.

Material
This is very much similar to androids design guidelines but now theres a blurred UI and from iOS which adds a frosted glass effect to windows. Apps can utilize this to make some of their elements like menus, tabs, taskbar, timeline semi transparent or make whole apps fully transparent.

Scale
this is essentially enhancing cross device support so that apps can scale on different devices with different input devices. It also changes the way apps will change or scale in Hololens platform so apps can scale in 3D and utilize Z axis of the space.

This is a gradual update and will come as stages in upcoming updates starting this fall. Some of the changes are already rolled out to Insiders (which is essentially beta testing for windows). Native apps like people, calculator and voice recorder apps are already using fluent design and have transparency and new animations to them.