From OpenStreetMap Wiki
|amenity = ticket_validator|
|A device which validates public transport tickets|
|Used on these elements|
|Tools for this tag|
|This tag page is a stub. You can help OpenStreetMap by expanding it.
Similar pages for structural reference: Tag:railway=tram, Tag:waterway=dock.
A ticket validator (also known as ticket puncher, punching machine, ticket marker) is a device that allows to validate a public transport ticket. See examples on Wikimedia Commons.