Pages in concrete5
In concrete5 we call individual pages, Pages. Simple, isn't it? Although Drupal also "makes pages", it does not really use pages as data object nor do we really work directly with pages in the Drupal system, instead we make nodes, or other entities, and pages are built from them. So the comparison I'll make here is between concrete5 Pages and Drupal Nodes. This is because concrete5 takes a much simpler approach to this entire aspect of the system. So instead of making Nodes, and then assembling 1 or more Nodes into a page the way Drupal does, concrete5 simply builds pages. Each page in concrete5 can have attributes assigned to it, which is roughly equivalent to Drupal Fields that are added to Content Types. In addition, concrete5 Page Types are each assigned a theme for presentation.
Nodes in Drupal
Drupal Nodes are essentially "Content Data Objects", and a Drupal site can have multiple "Content Types" which allow Nodes to be differentiated. concrete5 has similar capabilities using "Pages" and "Page Types". So suppose you want to display vehicle listings on your site. In Drupal you might create a Content Type named "vehicle listing". In concrete5 you would create a Page Type named "vehicle listing". In Drupal you would create vehicle listing Nodes, which Drupal would build into unique URL's, or pages. In concrete5 each time you add a new vehicle you would make a new Page using the Page Type "vehicle listing". So both systems have a way to achieve similar things, although they present vastly different management approaches.
The concrete5 Site Tree
The result of making concrete5 pages is that you will have a "Site Tree". This is a tree of all your site pages. In order to edit a page you can either navigate to its URL, or find it in your site tree. The site tree might be easier if your editing a group of similar pages. This compares roughly to the Drupal Content Admin where all the content items are listed.