You can use a custom WP_Query object that only returns posts that have a particular value in a custom field, for instance. You could also retrieve the custom field values for display on your site.

Here is how to alter your WordPress search results page to exclude certain posts based on the value of a custom field. It uses the pre_get_posts action hook.

WordPress.org took control of WP Engine’s Advanced Custom Fields plugin, forking and renaming it “Secure Custom Fields.” ...