Technical writers write... well, technical documents. Duh.

 http://www.klariti.com/technical-writing/What-is-Technical-Document.shtml

This article gives a definition of what a "technical document" is.  This relates to the class in the simplest of ways- a technical document is what technical writers write.  While in the olden days this was putting a pen to paper and cranking a story out, today it's much more technology-driven.  With the internet, things like blogs, emails, and websites allow for technical writing to be virtually everywhere.  You can even find entire magazines (like Wired) online.  

As far as what technical documents actually are, the best definition that the article gives is that a technical document is the "presentation of information that helps the reader solve a particular problem."  While this problem can be literally anything from how to write technical documents to how to build a pirate ship (see how I worked that in there?), it's end goal is the same.  Being able to get this information across in a clear, logical, and meaningful way is what this class is all about.