Neutron is an OpenStack project to provide "network connectivity as a service" between interface devices (e.g., vNICs) managed by other OpenStack services (e.g., nova). It implements the OpenStack Networking API.
This documentation is generated by the Sphinx toolkit and lives in the source tree. Additional documentation on Neutron and other components of OpenStack can be found on the OpenStack wiki and the Neutron section of the wiki. The Neutron Development wiki is also a good resource for new contributors.