A package is a folder that has been flagged specially so that the Finder presents it to the user as a single document. This discourages users from messing with the implementation details accidentally, while making it easy to do so if the need arises.
- Resources (strings, images, code, etc) are now stored as discrete files instead of byte ranges within a single file (the document's resource fork). This reduces the need for special resource editors and APIs to access the resource fork -- no more need for ResEdit.
- Developers (and users) can manipulate the contents of a package in the Finder by invoking the "Show package contents" contextual menu (right click) command.