This article “Better living through Taxonomies” gives a really good clarification of taxonomies and controlled vocabularies. It explains the concepts very well and gives some examples also. I felt it was a nice refresher on what taxonomies are and why they are important.
And an example of a hierarchy (because visual examples are awesome):
An example of a term hierarchy might be:
- Computers and internet
- Internet software
- World Wide Web software
- HTML editors