A child theme is a theme that inherits the functionality and styling of another theme, called the parent theme.
Child themes are the recommended way of modifying an existing theme.
WordPress Codex gives us a great explanation of using Child Themes:
There are a few reasons why you would want to use a child theme:
- If you modify a theme directly and it is updated, then your modifications may be lost. By using a child theme you will ensure that your modifications are preserved.
- Using a child theme can speed up development time.
- Using a child theme is a great way to learn about WordPress theme development.
Что собой представляет дочерняя тема?
Дочерняя тема может содержать один единственный файл – style.css, в котором указано название этой (Theme Name) и родительской (Template) тем, а также импортирован основной файл стилей родительской темы.
You can find more information about child themes on WordPress Codex.