When an application requests the ability to edit on my behalf there is an unordered list with the rights.
But when an app requests basic rights there is only a plain text message saying app "X" requests basic rights. I have no idea what that means. As a developer I'm hoping that means reading. As a user, I'd think "basic" includes editing as well, and I really don't want to grant certain apps that permission (e.g. the kind of tools that abuse OAuth as a way to do OpenID).
Digging back into overview of what these rights mean was hard. After granting access, I found the special page via the Preferences page, then "manage access" which listed "Basic rights" and had a linked list item to https://meta.wikimedia.org/wiki/Special:OAuth/grants#useoauth
That's where I finally found the information.