WordPress at a glance
filter is not described

the_search_query filter-hook . WP 2.3.0

Filters the contents of the search query variable for display.

Usage

add_filter( 'the_search_query', 'filter_function_name_7138' );
function filter_function_name_7138( $search ){
	// filter...

	return $search;
}
$search(mixed)
Contents of the search query variable.

Where the hook is called

the_search_query()
wp-includes/general-template.php 3599
echo esc_attr( apply_filters( 'the_search_query', get_search_query( false ) ) );

Where the hook is used (in WP core)

Does not used.