Definition of Raster graphics:
Computer (digital) image which (unlike vector graphics) is made up of small tiles (pixels or dots). When a raster image is enlarged, the pixels or dots give a stairstep-like jagged appearance. All video (monitor) screens, dot matrix, inkjet, and laser printers, and scanners are raster image devices whereas a plotter (pen-plotter) is a vector image device.
Meaning of Raster graphics & Raster graphics Definition