The highest-level checker grouping is referred to as a taxonomy. Any checker subgroups (below the taxonomy level) are referred to as categories. The issue category is used to group related issue types in default taxonomies (C/C++, Java and C#) and in custom taxonomies (if desired). For example, for the C/C++ taxonomy, the "Attempt to use Memory after Free" category contains issue types such as CL.FFM.ASSIGN and CL.FFM.COPY, among others.
Klocwork's downloadable MISRA C and MISRA C++ taxonomies do not contain categories.
"Categories" is a report property in the Category Details and Trending by Category reports in Klocwork Static Code Analysis. Taxonomy is the highest-level category appearing in these reports, but if a taxonomy contains categories, these will be listed for each applicable taxonomy.