W3C Official Glossary

I teach HTML at Santa Rosa Community College in Santa Rosa, CA. In the 
class textbook and in other sources I find that some HTML terms are used 
interchangeably. A tag is an element. A rule is a style. A class is a 
selector.

So I went to the W3.org site as a means to find specificity. Instead I 
found you have a glossary that includes several dozen reference works. 
Among them I find disagreement.

What I would like to know then: Is there an official W3C glossary? If 
so, what is its URL? If there is no official W3C glossary, can you 
recommend a single reference?

Thank you,

Jeff Sengstack