What is "bayerwald-ticket"

The Bayerwald-Ticket (lit: Bavarian Forest ticket) is a special, low-cost, local railway ticket introduced in 1999 for the counties ( Landkreise) of Regen and Freyung-Grafenau in the Bavarian Forest in southeast Germany. Until 2003 it was only valid between May and October; from 2004 it has been valid all-year round.