WordPress at a glance
action is not described

load-(pagenow) action-hook . WP 2.1.0

Fires before a particular screen is loaded.

The load-* hook fires in a number of contexts. This hook is for core screens.

The dynamic portion of the hook name, $pagenow, is a global variable referring to the filename of the current page, such as 'admin.php', 'post-new.php' etc. A complete hook for the latter would be 'load-post-new.php'.

Usage

add_action( 'load-(pagenow)', 'action_function_name_9739' );
function action_function_name_9739(){
	// action...
}

Where the hook is called

In file: /wp-admin/admin.php
load-(pagenow)
wp-admin/admin.php 332
do_action( "load-{$pagenow}" );

Where the hook is used (in WP core)

wp-includes/update.php 746
add_action( 'load-plugins.php', 'wp_update_plugins' );
wp-includes/update.php 747
add_action( 'load-update.php', 'wp_update_plugins' );
wp-includes/update.php 748
add_action( 'load-update-core.php', 'wp_update_plugins' );
wp-includes/update.php 752
add_action( 'load-themes.php', 'wp_update_themes' );
wp-includes/update.php 753
add_action( 'load-update.php', 'wp_update_themes' );
wp-includes/update.php 754
add_action( 'load-update-core.php', 'wp_update_themes' );
wp-admin/includes/admin-filters.php 50
add_action( 'load-tools_page_export_personal_data', '_wp_privacy_requests_screen_options' );
wp-admin/includes/admin-filters.php 51
add_action( 'load-tools_page_remove_personal_data', '_wp_privacy_requests_screen_options' );
wp-admin/includes/admin-filters.php 122
add_action( 'load-plugins.php', 'wp_plugin_update_rows', 20 ); // After wp_update_plugins() is called.
wp-admin/includes/admin-filters.php 123
add_action( 'load-themes.php', 'wp_theme_update_rows', 20 ); // After wp_update_themes() is called.
wp-admin/custom-background.php 70
add_action( "load-$page", array( $this, 'admin_load' ) );
wp-admin/custom-background.php 71
add_action( "load-$page", array( $this, 'take_action' ), 49 );
wp-admin/custom-background.php 72
add_action( "load-$page", array( $this, 'handle_upload' ), 49 );