Child Themes – Inherit the functionality of the parent theme
Templates – PHP source files used to generate the pages requested by visitors, and are output as HTML.
Template Hierarchy – To provide special-purpose Template files to override index.php.
Reserved Theme filenames – Filenames you should not use; these are special file names WordPress reserves for specific purposes.
Theme Review – if you are publicly releasing a Theme by submitting it to the Themes Directory.
Using Themes – Technical aspects of writing code to build your own Themes rather than how to activate Themes or where to obtain new Themes.
2010dev.wordpress.com – Twenty Ten | Just another WordPress theme
2012dev.wordpress.com – 2012 WordPress Theme dev | Just another WordPress.com site