Chikatetsu (地下鉄) means 'subway,' 'underground train,' or 'tube.' It's a train system that primarily runs underground, especially common in large cities for efficient public transportation. For example, '地下鉄で駅まで行きます' (I go to the station by subway).

地下を走る「電車」のことです。都会の交通手段によく使われます。例：地下鉄に乗ります。