WordPress custom fields are metadata used to add extra information to the post or page you are editing.
By default, when you write a new post, page, or any other content type, WordPress saves that content in two different parts.
The first part is the body of your content that you add using the WordPress content editor.
The second part is the information about that content. For example, the title, author, date, time, and more. This information is called metadata.
A WordPress website automatically adds all the required metadata to each post or page you create. You can also create and store your own metadata by using custom fields.