A megapixel is one million pixels — the tiny dots that make a digital picture. Camera shops and phone ads use the number to talk about how detailed a photo can be: a 12-megapixel camera makes a picture out of about twelve million dots. People often hear a bigger number and think better camera, and advertising leans on that, though actually the size of the sensor, the lens, and the light can matter more than the count; a small cheap sensor packed with dots can still look grainy. You meet the word with cameras, phone cameras, and sometimes screens. Informal speech may clip it to something like 48 megs; packs and specs write MP. It is a count of picture-dots, not a weight, and it does not by itself tell you if a picture will look beautiful.