A heritage railway is a term used, especially in Great Britain, for a railway which is run as a tourist attraction and is usually but not always run by volunteers, and seeks to re-create railway scenes of the past.
Heritage railways are usually railway lines which were once run as proper commercial railways, but were later no longer needed, or were closed down, and were taken over or re-opened by volunteers.
Typically a heritage railway will use steam locomotives, and old-fashioned rolling stock, to create a period atmosphere.
There are an especially large number of heritage railways in the United Kingdom due to the large number of railway lines that were closed in the 1960s, and British people's liking for railways. But many other countries have them as well.
See: List of heritage railways, Heritage railways in England