What is a Cricut Cartridge?
A Cricut cartridge is a portable memory device that is centered on a theme or subject and contains a variety of pictures, fonts and phrases. It also has creative features to enhance images by shadowing them, layering, and many others, depending on the theme. There are also three-dimensional objects you can choose and construct as well. The cartridge can be inserted into a Cricut machine, which allows you to choose the particular image that you want, which then prints and cuts it for you.
They are somewhat superficially divided into 6 categories:
UPDATE: It seems as though a new category was introduced recently: Cake cartridges; to be used with the new Cricut Cake machine (which looks to be a modified Cricut Expression).
These images and patterns on these cartridges are too detailed to be cut out by hand, but are no problem for a Cricut machine to handle. They help the busy scrapbooker to create projects in imaginative, unexpected ways.