MDPI refers to a medium-density screen (about 160 dpi) used on an Android device.
Term or suffix used in Android that stands for medium density displays. -mdpi can be added to layout, drawable, etc. folders in order to maintain artifacts that have especially been designed for this density.
Beside mdpi, one might use ldpi, hdpi or xhdpi, too. The Android system automatically chooses the appropriate resource files.
See official documentation for more.
