These are modules that the core ansible team maintains and will always ship with ansible itself. They will also receive slightly higher priority for all requests than those in the “extras” repos.
The source of these modules is hosted on GitHub in the ansible-modules-core repo.
If you believe you have found a bug in a core module and are already running the latest stable or development version of Ansible, first look in the issue tracker at github.com/ansible/ansible-modules-core to see if a bug has already been filed. If not, we would be grateful if you would file one.
Should you have a question rather than a bug report, inquiries are welcome on the ansible-project google group or on Ansible’s “#ansible” channel, located on irc.freenode.net. Development oriented topics should instead use the similar ansible-devel google group.
Documentation updates for these modules can also be edited directly in the module itself and by submitting a pull request to the module source code, just look for the “DOCUMENTATION” block in the source tree.