GTFS (General Transit Feed Specification)
A data specification that allows public transport operators to publish their transit data in a format that can be consumed by a wide variety of software applications. Today, the GTFS data format covers both static and real-time data and is used by thousands of public transport providers.
GTFS was originally written by Google and is similar to the TransXChange and SIRI formats used widely in the UK. Many public transport operators release this data as open data. A good source of GTFS data in the UK is Passenger’s open data portal.