Cluster bombs are also classified as conventional bombs insofar as they are not nuclear bombs. There are, however, many kinds of conventional bombs, including armor-piercing, fragmentation and incendiary bombs. Among these, the cluster type is a particularly vicious weapon if used against massed troops.
Each bomb usually contains hundreds of bomblets. After the bomb is dropped, it rotates along the horizontal axis. (See the diagram given above.) A small explosive charge opens the casing, and the centrifugal force of the spinning bomb distributes the bomblets far and wide. When dropped properly from the optimum altitude, the cluster bomb will kill anyone within an area of about 5,300 square meters. The bomblets themselves are often pre-fragmented so as to split them into dozens of sharpnels. Obviously, they cause particular harm to human targets.
Cluster munition (Wikipedia)