Raster printing refers to the method of printing which uses the raster image processor. The raster printing usually produces a raster image called a bitmap.

raster image = monitor, laser printer or ink-jet printer

vector image = graphics plotter

The most informative I could find on raster images is at the related link below.

A bitmap graphic is also known as a raster image.

Digital printing begins with creation of the document file ‰ÛÒ the words and images that will print on the page. Regardless of what program is used to create the file or any of its components, the file is converted into a raster graphics image. A raster is a grid of x and y coordinates on a display space; a raster image file identifies which of those coordinates to illuminate. A raster image file is sometimes referred to as a bit map because it contains information that is directly mapped to the display grid. BMP, TIFF, GIF and JPEG are all examples of raster image file types. The action of converting a file to a raster image file is known as raster image processing or RIPping.