D defs.my
Entry 1 sense Webster, 1913

event horizon

/ĭv-ĕnt' hẽr-īz'-ən/ · e·vent· ho·ri·zon · IPA /əˈvɛnt həˈɹaɪ.zən/
01 n. the boundary surface surrounding a black hole, from outside of which nothing inside can be observed, because nothing inside that surface, e…
  1. 1.
    the boundary surface surrounding a black hole, from outside of which nothing inside can be observed, because nothing inside that surface, even light, can escape beyond it. See also black hole and escape velocity.(Physics, Astron.) See: black hole, black hole, escape velocity