Today I confused someone by referring to the XML that was generated by the XLS… and not to forget the fact that the XML is styled by the XSLT. I ended up having to explain the whole process again – and explained each individual concept.
XML
Extensible Markup Language
Purpose: Structured way of saving information
Sharepoint example: a list/library
XSL
Extensible Stylesheet Language
Purpose: Stylesheets for XML
SharePoint example: ItemStyle.xsl, with styles for the CQWP
XSLT
Extensible Stylesheet Language Transformations
Purpose: Translates XML to something understandable for people
SharePoint example: transformations done to variables within ItemStyle.xsl (e.g. date)
And of course…
XLS
File format for MS-Excel.
Purpose: structured way of editing data graphically
SharePoint example: erm…. edit in data sheet?
I think that the W3Schools article on XSL Languages explains it well, too.