Big Dumb Booster (BDB) is a general class of launch vehicle based on the premise that it is cheaper to operate large rockets of simple design than it is to operate smaller, more complex ones regardless of the lower payload efficiency. As referred to by the Office of Technology Assessment:

The term Big Dumb Booster has been applied to a wide variety of concepts for low-cost launch vehicles, especially those that would use "low technology" approaches to engines and propellant tanks in the booster stage. As used here, it refers to the criterion of designing launch systems for minimum cost by using simplified subsystems where appropriate.

Even though the large minimum-cost design (MCD) booster is less efficient for all around operation, its total cost of operation is cheaper because it is easier to build, operate and maintain, with the benefit of high reliability because of reduced parts counts.