The pixel size of a digital image is specified in one of two ways—by its dimensions in pixels or by the total number of pixels it contains. For example, the same image can be said to have 4368 × 2912 pixels (where “×” is pronounced “by” as in “4368 by 2912), or to contain 12.7 million pixels (4368 multiplied by 2912). Since the term “megapixel” is used to indicate 1 million pixels, an image with 12 million pixels can also be referred to as a 12 megapixel image.
No matter how many pixels an image has, when you enlarge it enough, it begins to loose sharpness and eventually the pixels begin to show—an effect called pixelization. The more pixels an image has, the larger it can be displayed or printed before pixelization occurs.