The administrator can define keywords which can be used to tag and categorise bugs. For example, the keyword "regression" is commonly used. A company might have a policy stating all regressions must be fixed by the next release—this keyword can make tracking those bugs much easier. Keywords are global, rather than per product.
Keywords can be created, edited, or deleted by clicking the "Keywords" link in the admin page. There are two fields for each keyword—the keyword itself and a brief description. Currently keywords cannot be marked obsolete to prevent future usage.
This documentation undoubtedly has bugs; if you find some, please file them here.