node.module, line 1505
The node_permission() function defines permissions: e.g. "View published content" with the machine name "access content".
I'm guessing that "access content" is legacy, and "View published content" is much clearer for a site admin. However it's a little confusing for (new) module developers that the displayed permission names don't match what you need to put in the access arguments array.
Maybe the official names could be displayed alongside in the Permissions page when the two values differ? Or the proper values could be listed in the API/documenation.