There are two similar but different types of Coble hypersurfaces.
The Kummer variety of the Jacobian of a genus 3 curve can be embedded in 7-dimensional projective space under the 2-theta map, and is then the singular locus of a 6-dimensional quartic hypersurface (Coble 1982), called a Coble hypersurface.
Similarly the Jacobian of a genus 2 curve can be embedded in 8-dimensional projective space under the 3-theta map, and is then the singular locus of a 7-dimensional cubic hypersurface (Coble 1917), also called a Coble hypersurface.
Coble, Arthur B. (1982) [1929], Algebraic geometry and theta functions, American Mathematical Society Colloquium Publications, vol. 10, Providence, R.I.: American Mathematical Society, ISBN 978-0-8218-1010-1, MR 0733252