As mentioned in Chapter 3, template overrides are specialized files the Joomla! system checks for in your template's
html folder. Template overrides include module chrome and component overrides. If Joomla! discovers that a particular file exists, for a specific module or component, in your template's
html folder, Joomla! will reference that file's output, rather than its core output. The most common approach is to use the Beez template overrides, if you'd like to have truly accessible, table-less XTHML output from Joomla!. You can also create your own files.
Of course, the Joomla! system is not "psychic"! You can't just create an override and place it anywhere in your template directory, named anything you want, and hope Joomla! ...