Resources is a collective term for the projects, folders, and files that exist in the Eclipse PDT. The navigation views provide a hierarchical view of resources and allows you to open them for editing. Other tools may display and handle these resources differently.
There are three basic types of resources that exist in the Eclipse PHP PDT:
Comparable to files as you see them in the file system.
Folders are similar to directories on a file system. In the Eclipse PDT, folders are contained in projects or other folders. Folders can contain files and other folders.
Contain folders and files. Projects are used for builds, version management, sharing, and resource organization. Like folders, projects map to directories in the file system. (When you create a project, you specify a location for it in the file system.)
A project is either open or closed. When a project is closed, it cannot be changed in the Eclipse PDT. The resources of a closed project will not appear in the Eclipse PDT, but the resources still reside on the local file system. Closed projects require less memory. Since they are not examined during builds, closing a project can improve build time.
When a project is open, the structure of the project can be changed and you will see the contents.
Folders and files directly below projects can be linked to locations in the file system outside of the project's location. These special folders and files are called linked resources.
Different tools that plug into the Eclipse PDT use their own specialized types of projects, folders, and files.