The Collaborative International Dictionary
Block system \Block system\ (Railroads) A system by which the track is divided into short sections, as of three or four miles, and trains are so run by the guidance of electric, or combined electric and pneumatic, signals that no train enters a section or block until the preceding train has left it, as in
absolute blocking, or that a train may be allowed to follow another into a block as long as it proceeds with excessive caution, as in
Wiktionary
alt. (context railway English) A system of managing trains that breaks the line into small segments, and if a train is in a segment, no other train may follow, unless the second train is following the first, with caution.(R:MW3 1976: page=6) n. (context railway English) A system of managing trains that breaks the line into small segments, and if a train is in a segment, no other train may follow, unless the second train is following the first, with caution.(R:MW3 1976: page=6)