The density of the dots, known as the resolution, determines how sharply the image is represented. This is often expressed in dots per inch (dpi ) or simply by the number of rows and columns, such as 640 by 480.

To display a bit-mapped image on a monitor or to print it on a printer, the computer translates the bit map into pixels (for display screens) or ink dots (for printers). Optical scanners and fax machines work by transforming text or pictures on paper into bit maps.

Bit-mapped graphics are often referred to as raster graphics. The other method for representing images is known as vector graphics or object-oriented graphics. With vector graphics, images are represented as mathematical formulas that define all the shapes in the image. Vector graphics are more flexible than bit-mapped graphics because they look the same even when you scale them to different sizes. In contrast, bit-mapped graphics become ragged when you shrink or enlarge them.

Fonts represented with vector graphics are called scalable fonts , outline fonts , or vector fonts. The best-known example of a vector font system is PostScript. Bit-mapped fonts, also called raster fonts, must be designed for a specific device and a specific size and resolution.

msdn: Bitmap Class
The Bitmap class expands on the capabilities of the Image class by providing additional methods for creating and manipulating raster images.

The Code Project
A set of basic tutorials on working with the core bitmap structures.

Vectors And Bitmaps - Guide To Photoshop Basics.
Shop Talk is a beginner's guide to Photoshop that focuses on Photoshop basics.

Webopedia's Graphics Software Terminology
Graphics jargon is confusing. To help you better grasp this genre, we look at graphics software and define common terminology to help you work more easily with digital images.