Definition

A screencast is a recording of every action that happens on your computer screen. This recording can also be accompanied by an audio track or captions to explain the actions as they happen.

"Just as a screenshot is a picture of a user's screen, a screencast is essentially a movie of what a user sees on their monitor" from Wikipedia

Software examples

Proprietary
Adobe Captivate
Camtasia Studio

Freeware
Jing (with 2GB free hosting on screencast.com)
Wink

How can libraries use screencasts?

User education
Staff training

Useful links:
Kroski, Ellyssa. 2008. A quick guide to screencasting for libraries

Examples of libraries using screencasts:
Duggan Library (using YouTube as a host)

Ohio University - Biz Wiki (using Captivate and Wink)

Oxford University Language Centre (Jing) Introduction to the library catalogue & Visit to the virtual library for learning languages As I'm just testing right now, all comments welcome.

University of Waterloo (Wink)

University of Wisconsin Law Library (Jing)