It’s subtle – page to the bottom to see the sample user interface: What is Google’s Material Design for Android? Appvigil – Android App Security Scanner.
The software API’s provide new “shadow” features to enhance the Z-axis “elevation” dimension of a control or window. Details of the feature are available from Google.
These effects are – so far – very subtle. I am not sure of the point of this – its a basic element of graphic design that was used in software more than 25 years ago.
An “API” is an “application programming interface”. Operating systems – such as Android, Windows or Mac OS X – expose features to application programs through an interface, known as an “application programming interface” or just API.