hypersurface
generalization of the concepts of hyperplane, plane curve, and surface; a manifold or an algebraic variety of dimension n, which is embedded in an ambient space of dimension n+1
affine sphere
Mathematical concept
absolute horizon
boundary in spacetime, defined with respect to the external universe, events inside which cannot affect an external observer
apparent horizon
surface that is the boundary between light rays that are directed outwards and moving outwards, and those directed outward but moving inward
event horizon
the point of no return; boundary of a region of spacetime from which one cannot escape once entered
quartic threefold
degree 4 hypersurface of dimension 3 in 4-dimensional projective space
cubic threefold
hypersurface of degree 3 in 4-dimensional projective space
quadric
locus of zeros of a quadratic polynomial (affine or projective, not necessarily real)