This depends on the eCommerce system in use:
With Magento or Shopify: The CMS pages are fed to Klevu which then indexes the page title, description, meta keywords and description. It uses this content to retrieve the relevant CMS pages.
With a Blog CMS feed (for example Wordpress): The merchant has the flexibility to provide any relevant attributes and Klevu will index them.
Please see here for more information on providing a feed.