Essentially the categorization package allows you to define taxonomies of keywords that can then be used to categorize content (acs objects). It falls under the "knowledge management" umbrella. It provides UI for searching for objects that fall under specified categories. "give me all content that has been categorized as being related to OpenACS Tcl API for localization" that kind of thing.
By providing a generalized categorization package all such keyword assignment, management, navigation etc is handled consistently for objects created by any package, which means you can build sites in which all content can be searched by category etc.
