(US, rail transport) The accidental head-on collision of two trains.
(US, rail transport) Sometimes also used for a near-collision in the same situation.
From cornfield and meet: early collisions often occurred out in the country alongside a cornfield, rather than the trains passing safely in a station or siding. Originated in the U.S., in use since at least the 19th century.
English Wiktionary. Available under CC-BY-SA license.