This term refers to the size of an image, usually in reference to a photo from a digital camera or camera phone. Megapixel means one million pixels. The resolution of digital cameras and camera phones is often measured in megapixels. For example, a 5-megapixel camera can produce images with five million total pixels.
In simple words a megapixel is equal to one million pixels.
Digital images are made up of thousands of these tiny, tile-like picture elements. The more pixels, the higher the image resolution.