This global variable stores the requested page number of a multipage post that has to be shown. It is set in the function
setup_postdata($post) defined in [wordpress root folder]/wp-includes/functions.php. The variable
page in the WordPress request (query string) is used to set this global variable. The multipage content of the post is stored in the global variable pages.
page does not indicate the page number of a paginated archive, it is used only for a multipage post.
Plugin and theme developers can use this variable to identify the requested page number of the current post being displayed.
Back to full list of global variables.