Should tags, specifically excerpts, be descriptive or instructive?

Question

There are quite a few tags that need cleenup, better descriptions and wikis. My question is, should tags be descriptive of what they represent or rather convey some sort of instruction to the user.

Examples:

mosfet provides a clear explanation of what an mosfet is.

usb "USB=Universal Serial Bus. Specify which chip you are using, if applicable, in your question."

Notwithstanding that the usb tag is poor by any standards, should it be an instruction or an explanation? Another example: transistor

I quote Kortuk:

the wiki is to make it clear to the community what it means.

How does this relate to the excerpt?

EDIT:

I found this post by Jeff Atwood: http://blog.stackoverflow.com/2011/08/improved-tagging/

Answers this in part, but I still think that some tags are overly instructive and need some more flesh.

Answer 1

should tags be descriptive of what they represent or rather convey some sort of instruction to the user.

Definitely the latter, meaning the tag wiki should spend most of its time explaining how to use the tag properly.

It can do both, but the priority particularly in the excerpt is "when should I use, and not use, this tag?"

As you noted http://blog.stackoverflow.com/2011/08/improved-tagging/ is the proper guidance, we tried to make the tag wiki editing sidebar have an abbreviated form of this advice.