block system

== English == === Noun === block system (plural block systems) (rail transport) On railways, a system by which the track is divided into sections of three or four miles, and trains are run by the guidance of electric signals so that no train enters a section or block before the preceding train has left it. (mathematics) Given a group G that acts on a set X, a partition of X that is G-invariant. === References === “block system”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.