A Child Theme in WordPress is a sub-theme that receives all the functionality, features, and style of its parent theme. Child themes are a secure way to modify a WordPress theme. Without actually doing any changes to the WordPress parent theme’s files.
When the parent theme gets update, modifications made in the child theme are also preserve. And use on the update version as well.
This is why child themes are the most secure and best way to make changes to an existing WordPress theme. Rather than modifying theme files directly, you can override them with the templates in the child theme.
If you want to learn how to create child theme , read below article:
To make a child theme in WordPress, you must create a folder in your themes directory for your Child Theme. In this folder, the only main file you need is style.css.
In the header of the style.css file, you can specify the parent theme by adding a template line into the comment code. where the theme name is written previously.
Because this style sheet is include after the style sheet of the parent, it will override any styles in the parent theme’s style.css file.
Activate the Child theme before applying the modification on the site. The parent theme will still include any functionality that hasn’t been overwritten by the child theme.