apparent horizon
surface that is the boundary between light rays that are directed outwards and moving outwards, and those directed outward but moving inward
en-GB/əˈpæɹənt həˈɹaɪzn/
en-US/əˈpɛɹənt hɚˈaɪzən/
surface that is the boundary between light rays that are directed outwards and moving outwards, and those directed outward but moving inward