bitmap 
A method of depicting a graphic image on a computer screen, a printer, or a scanner. As its name suggests, a bitmap is a map of dots--similar to what you see when you look at a newspaper photo under a strong magnifying glass. Bitmaps come in many file formats (GIF, JPEG, TIFF, BMP, PICT, and PCX, to name a few) and can be read by paint programs and image editors such as Adobe Photoshop. If you scale up a bitmap, it will look blocky.