Q. What do you mean by Resolution?

Resolution is parameter which defines possible sharpness or clarity of a video image.  Resolution is defined as number of pixels which make up an image. These pixels are then spread across the height and width of monitor.  Resolution is independent of physical characteristics of monitor. The image is produced without thinking about the ultimate screen it is to be displayed upon.  Therefore unit of resolution is the number of pixels not the number of pixels per inch.  For illustration a standard VGA native graphic display mode has a resolution of 640 pixels horizontally by 480 pixels vertically.  Higher resolutions means the image can be sharper since it comprises more pixels. 

Actual on-screen sharpness is given as dots-per-inch and this relies on both resolution and size of the image.  For same resolution an image will be sharper on a smaller screen it implies that an image that may look sharp on a 15" monitor may be a little jagged on a 17" display.