Description 
 If the $page parameter is specified, this function will additionally check if the query is for one of the pages specified.
 For more information on this and similar theme functions, check out the  Conditional Tags article in the Theme Developer Handbook.
 See also 
     Parameters 
  - $page
-   (int|string|int[]|string[]) (Optional)  Page ID, title, slug, or array of such to check against.   Default value: '' 
Return 
 (bool) Whether the query is for an existing single page.
     Notes 
  - Will return true if an empty value is passed
- Due to certain global variables being overwritten during The Loop, is_page() will not work. In order to call it after The Loop, you must call wp_reset_query() first.
Source 
  File: wp-includes/query.php 
 function is_page( $page = '' ) {
	global $wp_query;
	if ( ! isset( $wp_query ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '3.1.0' );
		return false;
	}
	return $wp_query->is_page( $page );
}       Changelog 
     | Version | Description | 
    | 1.5.0 | Introduced. |