Hatch is the one that does not have a rear projection like the sedan that has a dicky.
You may fold the seat from the rear in a hatch and make room to keep more luggage that is not possible in a sedan.
At its most basic, the sedan is a passenger car with two rows of seats & adequate passenger space in the rear compartment for adult passengers. The vehicle most commonly has a separate trunk (boot in British English), for luggage at the rear. However, rear-engined sedans include models by Chevrolet, Tatra, & Volkswagen.
Hatchback is a term designating an automobile design, containing a passenger cabin with an integrated cargo space, accessed from behind the vehicle by a single, top-hinged tailgate or large flip-up window. The vehicle commonly has two rows of seats, with the rear seat able to fold down to increase cargo space.