From the overview:

NaPTAN provides a unique identifier for every point of access to public transport in the UK, together with meaningful text descriptions of the stop point and its location. This enables both computerised transport systems and the general public to find and reference the stop unambiguously. Stops can be related to topographic regions via the National Public Transport Gazetteer.

From NaPTAN Terms & Conditions:

The NaPTAN Database is Crown Copyright. Use of the NaPTAN data is subject to license by the Department of Transport. Public Sector and Commercial Licences are available. Fees may be charged for Commercial Licenses.

A subset of the NaPTAN data is available on Open Street Map. See the uk-naptan-osm package.