Big Dumb Boosters (BDB) are a general class of launch vehicle built around the idea that it is cheaper to mass build and operate a large, strong, heavy rocket of simple design than it is to build a few smaller, lighter, more cleverly-designed ones. Even though the large booster is less efficient for an all around operation, its total cost of operation is cheaper because it is easier to build, operate and maintain. As with all forms of mass production, it is likely that, as builders gain more experience with production of parts and construction, and more production infrastructure is established, costs may go down further. However, in having a bigger rocket, a smaller number of rockets need to be produced to launch a certain mass of payload into orbit, thereby working against mass production.
In general, Russian rockets are closer to the BDB concept than their US counterparts. US rockets tend to be built of the most modern, lightest materials available and to extremely tight tolerances, using often purpose-built custom parts, resulting in great expense. Many of them require very careful handling to avoid being damaged while on the ground. Russian rockets, on the other hand, tend to be built more heavily, and are easier to handle. They are built with larger margins of strength and to looser tolerances.
The BDB (Big Dumb Booster) plays a significant role in Stephen Baxter's Manifold series.