A dreadnought is a type of battleship with fast propulsion systems and an "all-big-gun" armament scheme. They are the heavy hitters of any fleet.
Dreadnoughts are huge vessels, carrying large complements of crew to handle their immense internal systems. They’re so massive that damage that would destroy a smaller starship usually doesn’t hurt a dreadnought much, and their armament is usually truly formidable.
Dreadnoughts pay for their firepower with typically abysmal speed and maneuverability characteristics and very high expense. Their expense usually limits their numbers, such that most navies may have only two or three starships that have been built on dreadnought chassis (if any at all). Expense of operation also limits the types of missions a dreadnought is typically employed for, and usually they will be found either in planetary defense or strike missions.