railway frog
Technical term in railway engineering for the crossing point of two rails where the flanges of train wheels pass through.
It is necessary to regularly inspect the wear of the railway frog.
Irregular kanji usage; 鉄 is a common substitute for the rare 轍, but this spelling is not standard.
The reading てっさ is a compound of 轍 (てつ, 'rut, wheel track') and 叉 (さ, 'fork, crossing'), describing the forked shape where rails cross. The exact historical derivation is uncertain.