| add_comment_meta() | Adds metadata (custom field) for the specified comment. |
| add_metadata() | Add metadata (an additional data) for the specified object (a post, a comment, a user etc). |
| add_post_meta() | Adds meta field to the specified post. |
| add_term_meta() | Adds metadata to a term. |
| add_user_meta() | Adds meta data to a user. |
| delete_comment_meta() | Remove metadata matching criteria from a comment. |
| delete_metadata() | Delete metadata for the specified object. |
| delete_post_meta() | Remove metadata matching criteria from a post. |
| delete_term_meta() | Removes metadata matching criteria from a term. |
| delete_user_meta() | Remove metadata matching criteria from a user. |
| get_comment_meta() | Retrieve comment meta field for a comment. |
| get_metadata() | Retrieve metadata for the specified object. |
| get_post_custom() | Retrieve post meta fields, based on post ID. |
| get_post_custom_keys() | Retrieve meta field names for a post. |
| get_post_custom_values() | Retrieve values for a custom post field. |
| get_post_meta() | Gets the value of the specified custom field of the post. Also can get an array of all post meta fields. |
| get_site_meta() | Retrieves metadata for a site. |
| get_term_meta() | Retrieves metadata for a term. |
| get_the_author_meta() | Retrieves the requested data of the current or requested user (post author). |
| get_user_meta() | Retrieve user meta field for a user. |
| has_term_meta() | Gets all metadata of the specified taxonomy element (term). |
| is_protected_meta() | Determines whether a meta key is protected (internal). |
| register_meta() | Registers a meta key. |
| register_post_meta() | Registers a meta key for posts. |
| register_term_meta() | Registers a meta key for terms. |
| sanitize_meta() | Sanitize meta value. |
| the_author_meta() | Outputs the field from the user's DB object. Defaults to current post's author. |
| the_meta() | Display list of post custom fields. |
| update_comment_meta() | Update comment meta field based on comment ID. |
| update_metadata() | Update metadata for the specified object. If no value already exists for the specified object ID and metadata key, the metadata will be added. |
| update_post_meta() | Updates specified meta field of specified post. Or adds it, if it's not exists. |
| update_term_meta() | Updates term metadata. |
| update_user_meta() | Update user meta field based on user ID. |
| wp_read_image_metadata() | Get extended image metadata, exif or iptc as available. |