Custom fields are used on WordPress sites as a way to allow post authors to include more information. Custom fields are also sometimes called post meta because the information is stored as meta data. The information added in custom fields can then be displayed on the WordPress theme by including certain template tags.
Custom fields can contain any information you want to share with readers. For example, you can list the music you’re currently listening to, a product rating, or any other information you feel would be helpful or relevant to your post.
WordPress, by default, hides custom fields. However, you can enable them by clicking on the button for Screen Options found in the top right part of the admin section. Click on the box next to Custom Fields to make the feature visible on the post editor.
By adding custom fields to your posts, you can extend the information included in your posts. Different plugins and themes also make use of custom fields to store different information. The meta data included for SEO purposes, for example, is saved in custom fields. Your meta data can even be entered through a different write-panel rather than the standard user interface.