Printing a bitmapped character is simply a matter of blasting the right bits out to the printer. There are a number of disadvantages to this approach. The bitmap represents a particular instance of the character at a particular size and resolution. It is very difficult to change the size, shape, or resolution of a bitmapped character without significant loss of quality in the image. On the other hand, it's easy to do things like shading and filling with bitmapped characters.
Outline fonts represent each character mathematically as a series of lines, curves, and ' hints '.
PostScript printers, for example, do this in the print engine. Many of the disadvantages that are inherent in the bitmapped format are not present in outline fonts at all. Because an outline font is represented mathematically, it can be drawn at any reasonable size. LaserJet .SFP and .SFL files, TeX PK, PXL, and GF files, Macintosh Screen Fonts, and GEM .GFX files are all examples of bitmapped font formats. PostScript Type 1, Type 3, and Type 5 fonts, Nimbus Q fonts, TrueType fonts, Sun F3, MetaFont .mf files, and LaserJet .SFS files are all examples of outline font formats.