A diamond junction (aka diamond crossover,diamond crossing or flat crossing) is a railway junction that has a track configuration in which merging or crossing railroad lines provide track connections with each other that require trains to cross over in front of opposing traffic at grade (i.e. on the level). Wikipedia
Compare with an ordinary crossover, which is a pair of switches that connects two parallel rail tracks, allowing a train on one track to cross over to the other. See crossover
See also Diamond Junctions and Setting Routes.