Tundra is the semi-frozen land found in the world's colder climates. It is less useful than plains or grassland, but slightly better than desert. Nobody builds cities in the tundra unless they're desperate for resources - or they've got nowhere else to go.
A clear Tundra tile will provide 1 Food if worked by a citizen.
A city with the Mass Digester building( Organics) adds 1 Energy to the yield, making tundra effectively the same as Coasts. However, farmland can only be built on tundra tiles next to a river or lake.