A Taxonomy is an organization system. It is a controlled vocabulary, containing a parent-child or hierarchical relationship, the specificity happens at the lower levels, at the branches, at the leaflets - or at the end of the list. They are very common on websites. They are also commonly supported as pick lists -- a drop down menu of ten or twelve items. Sometimes they are browsable directories. There are many different ways to put them in play. There are not many standards as yet for taxonomies but there are many standards for thesauri.