Template variables can be used to display dynamic content directly within content areas of a course - such as to display a student's name or a course title.
Mashups provide a way to hook into the Visual Text Box Editor to embed content from around the web directly inside of course content. Examples of mashups include the YouTube, Slideshare, and Flickr mashups that ship with the core product.
Building your own mashup is easy. You'll need to code the screens providing the logic to search for videos and then return the embed code back to the WYSIWYG editor. There is a presentation available from the 2010 Developers Conference that describes how: http://www.edugarage.com/display/BBDN/Blackboard+Developers+Conference+2010+presentations
There are also several sample mashup projects available on the edugarage sample code page: http://www.edugarage.com/display/BBDN/Sample+Code
In addition, there are two open source projects that you can reference for even more working source code: http://projects.oscelot.org/gf/project/jingmashup/ and http://projects.oscelot.org/gf/project/bb_wordpaste/