Node ID: unique identifier for each node. It can be found in the path of the node. For example, a node with the path "http://drupal.org/node/414", has for node ID "414".
Drupal names any content that it manages a "node". An article page will for example be a node. This node will have a type: forum, feature article, brief information, tutorial, blog, comment, input form, collaborative book, image or image gallery, interactive survey, wiki page, etc. : the shape is no longer subject to a predetermined architecture, which makes the content easily reconfigurable. This node will also possess fields: name, type, date, author, possible image, body, community votes on its content, etc.
The Node Comments module allows comments on all types of content. It is possible to set the display of these comments according to the design of the site.