HDPI refers to a high-density screen (about 240 dpi) used on an Android device.
Screen is a display, or a monitor
50px larger resolution
"So as i said - mdpi also doesn t means that your screens resolution is less than hdpi screens resolution"
from question "When designing a UI interface for MDPI and HDPI ANdroid how do i beat the height issue?"
"Even if i create three versions for ldpi mdpi and hdpi there are more than screens resolutions in that table if there is no matching image it will scale my image and may not retain the aspect ratio"
from question "Android Background Image: How to Support All Resolutions?"
"If in java code the values would be in pixels so 50px on mdpi screens will look larger than on hdpi screens"
from question "Having trouble getting my head around UI Graphics android"
"Edit - now that i think about it i m not sure why your image would appear smaller unless your screens had a greater dpi than hdpi"
from question "Why are my project's drawables blurry?"
"I am not aware of any device that can use api 14 with a screens density lower than hdpi"
from question "If I support a minimum of API 14, what screen densities do I not have to worry about?"