The excerpt meta box allows working with the post_excerpt field. By default, is used only in posts and attachments.
Excerpt
Adding excerpts to Pages
By the Web Warlock, Wednesday, 28/Jul/2010 3:47
To add excerpts to Pages, from 3.0 on you just need to add the support for the excerpt
feature for the page
post type with add_post_type_support called in the init
hook.