WordPress at a glance
function is not described

wp_plugin_directory_constants() WP 3.0.0

Defines plugin directory WordPress constants

Defines must-use plugin directory constants, which may be overridden in the sunrise.php drop-in

No Hooks.

Return

Nothing (null).

Usage

wp_plugin_directory_constants();

Code of wp plugin directory constants: wp-includes/default-constants.php VER 5.0.3

<?php
function wp_plugin_directory_constants() {
	if ( !defined('WP_CONTENT_URL') )
		define( 'WP_CONTENT_URL', get_option('siteurl') . '/wp-content'); // full url - WP_CONTENT_DIR is defined further up

	/**
	 * Allows for the plugins directory to be moved from the default location.
	 *
	 * @since 2.6.0
	 */
	if ( !defined('WP_PLUGIN_DIR') )
		define( 'WP_PLUGIN_DIR', WP_CONTENT_DIR . '/plugins' ); // full path, no trailing slash

	/**
	 * Allows for the plugins directory to be moved from the default location.
	 *
	 * @since 2.6.0
	 */
	if ( !defined('WP_PLUGIN_URL') )
		define( 'WP_PLUGIN_URL', WP_CONTENT_URL . '/plugins' ); // full url, no trailing slash

	/**
	 * Allows for the plugins directory to be moved from the default location.
	 *
	 * @since 2.1.0
	 * @deprecated
	 */
	if ( !defined('PLUGINDIR') )
		define( 'PLUGINDIR', 'wp-content/plugins' ); // Relative to ABSPATH. For back compat.

	/**
	 * Allows for the mu-plugins directory to be moved from the default location.
	 *
	 * @since 2.8.0
	 */
	if ( !defined('WPMU_PLUGIN_DIR') )
		define( 'WPMU_PLUGIN_DIR', WP_CONTENT_DIR . '/mu-plugins' ); // full path, no trailing slash

	/**
	 * Allows for the mu-plugins directory to be moved from the default location.
	 *
	 * @since 2.8.0
	 */
	if ( !defined('WPMU_PLUGIN_URL') )
		define( 'WPMU_PLUGIN_URL', WP_CONTENT_URL . '/mu-plugins' ); // full url, no trailing slash

	/**
	 * Allows for the mu-plugins directory to be moved from the default location.
	 *
	 * @since 2.8.0
	 * @deprecated
	 */
	if ( !defined( 'MUPLUGINDIR' ) )
		define( 'MUPLUGINDIR', 'wp-content/mu-plugins' ); // Relative to ABSPATH. For back compat.
}