What is a Megapixel?
A megapixel (abbreviated MP) is 1 million pixels. We say an image has 4 megapixels when it has 4 million pixels in total. For example, an image with 1000 pixels in width by 4000 pixels in height has 4 million pixels in total, so it's a 4 megapixel image. Similarly, we say a smartphone's camera is 4 megapixels when the images it takes are stored as files with 4 million pixels in them.