What is SQL (Structured Query Language) and how is it important for the web site? (A question from a member)
Data and Databases.

A Phone Directory holds data as a flat file, you search by city then alphabetically by name.
In the U3a Web Site the CSS file, (Cascading Style Sheet) is a flat file database as well as is the Windows Registry.
A web page can consist of a flat file, which can call other web pages in a structured order that normally never varies.

The U3A Web Site is more dynamic, where pages can be published and unpublished without having to adjust other pages. This is achieved using Joomla! to link and unlink pages. The page data is held in a Relational Database.
Terry Hawker wrote an excellent description of a Relational Database, read it here.

SQL (Structured Query Language) is one language used to communicate with a Relational Database which uses tables to store the web site data.