This short recipe contains only a few lines of code which register a function to be called when WordPress is preparing meta boxes for all the administration sections, followed by the implementation of this function. The function itself makes two calls to the remove_meta_box function to remove the custom fields section from the post and page editors. This function requires three parameters:

remove_meta_box( $id, $page, $context );  

The first argument is the meta box identifier that was used when it was first created. While you may not know where the creation code for a given meta box is located within the WordPress source code, a quick look at the box's div id in the page source from a browser reveals its name. In this case, the id is postcustom. The other two arguments indicate the name of the editor from which the meta box is to be removed and the context of the meta box (normal, advanced, or side).

Once the plugin is activated, the designated box disappears from the interface immediately.