WordPress has the ability to allow post authors to assign custom fields to a post. This arbitrary extra information is known as meta-data.
$custom_field = get_post_meta($post->ID, 'custom-field', true); if($custom_field) {echo $custom_field;}
https://codex.wordpress.org/Custom_Fields#Usage
https://codex.wordpress.org/Custom_Fields#Displaying_Custom_Fields
Learn more – https://codex.wordpress.org/Custom_Fields