Magento 2.0.18 is the final 2.0.x release. After March 2018, Magento 2.0.x will no longer receive security patches, quality fixes, or documentation updates. To maintain your site's performance, security, and PCIPayment Card Industry: Refers to debit and credit cards and their associated businesses. compliance, upgrade to the latest version of Magento.
The page hierarchy system uses nodes to identify related pieces of content, and to organize content pages into a parent/child relationships. A parent node is like a folder that might contain child nodes and pages. The relative position of each node and page in the hierarchy is shown as a tree. A node might contain other nodes and content pages, and a single content page might be associated with multiple nodes and other content pages in a parent/child or neighbor relationships.