Over the past few years the popularity of flat design has soared with the likes of Google shifting their logo from a material design to a flat design.
Material design was originally used to fix some of flat design’s usability problems by adding padding, depth, lighting and shadows to add a hint of realism to the design, material design standards were developed by Google and can be found here.
Flat design features no three-dimensional elements and has no stylistic features that imply any dimensions, making it appear as though it is lying flat, hence the name.
Take a look at Google’s logo development to see how their design has developed: