Trainers and instructional designers sling around the term "storyboarding," as if it is a process that is unique to our field. The term tends to sound a bit mysterious to clients and others outside of our circle, although other professions use similar approaches.
At its essence, storyboarding is a method used to sketch out content at a high level in order to validate flow, find gaps, and iron out complicated areas. Walt Disney is often credited as inventing storyboards for his animations.
Instructional designers use storyboarding to sketch out content for courses that are ultimately delivered through various formats, such as by an instructor or online. The storyboard defines content, slide by slide or screen by screen, to show the progression of learning topics, and can be developed in PowerPoint, Word, a special storyboarding tool, etc.
Many designers use a two column format, with slide or screen text in the left column and either detailed instructor notes or, for online learning, a narration script in the right column. Here are some free storyboard templates for you to check out: http://theelearningcoach.com/resources/storyboard-depot/
For elearning, the storyboard also contains notes on graphic ideas for the developer who puts together animations and visual presentation of the content using tools such as Flash. For instructor-led training, the narrator script is replaced with instructor notes, which provide more detailed talking points than the content that appears on the slides. Instructor-led presentations are often developed in PowerPoint, which allows the instructor to update the content as he or she gains classroom experience with presenting the content.
Now that you know about storyboards, I bet you can see the similarity to screen mockups or can envision storyboards used for web sites.