It's arguable whether or not User Stories is the best name for this concept, but it's a little late to worry about that.  My advice is to not worry too much about the precision of what is a user story, but concentrate on the spirit.

=== A user story makes a difference to a user of the system. ===
It does something a user wants (or avoids something the user doesn't want).

"Have my data available when I log into the system tomorrow" is a user story.  "Write the data to the database" is not; it's a technical task.

"Don't crash when the zip code field is left blank" is a user story.  "Validate input" is not.

=== A user story is functional ===
It slices through the system, involving all the layers and subsystems as needed.


== Splitting stories ==
 * My own [[http://idiacomputing.com/pub/UserStories.pdf|handout on user stories]]
 * William Wake's [[http://xp123.com/xplor/xp0512/index.shtml|Twenty Ways to Split Stories]] (now available in [[http://xp123.com/xplor/split-summary/index.shtml|PDF summary]])
 * Lasse Koskela's [[http://radio.javaranch.com/lasse/2008/06/13/1213375107328.html|Ways to split user stories]] which refers to J.B. Rainsberger's [[http://jbrains.ca/permalink/5|Splitting stories: an example]]
 * James Grenning's [[http://www.renaissancesoftware.net/blog/archives/48|Story Weight Reduction Toolkit]]
 * Richard Lawrence's [[http://www.richardlawrence.info/2009/10/28/patterns-for-splitting-user-stories/|Patterns for Splitting User Stories]]