Meaning
A Child Theme is a theme that depends on another theme (Parent Theme), inheriting its functionality and styling while enabling customization that survives parent theme updates.
Definition
Child Themes solve a critical problem: when you customize theme files directly and the theme updates, your changes are lost. Child Themes maintain separate customization files that override parent theme templates and styles without modifying the original theme.
A child theme requires only two files to function: style.css (with proper headers declaring the parent theme) and functions.php (for enqueueing parent styles and custom functionality). Additional template files added to the child theme automatically override matching parent theme files.
This architecture allows using premium themes or framework themes (Genesis, Thesis) while making unlimited customizations that remain intact through parent theme updates. It’s considered best practice for any theme customization beyond basic Customizer settings.
Example
A designer purchases Astra Pro theme (parent) and creates an Astra Child theme for client customization. They copy single.php to the child theme directory and modify the post layout, add custom CSS in the child theme’s style.css, and include custom functions in functions.php. When Astra Pro releases security updates, the client updates the parent theme safely, all child theme customizations remain untouched.
