A bridged bicycloalkane is a bicycloalkane whose molecule has two carbon atoms shared by all three rings identifiable in the molecule. The two carbon atoms shared by the three rings are called bridgehead carbon atoms. A bond or a chain of bonds connecting the bridgehead carbon atoms is called a bridge.
eg. 1: Decalin
eg. 2: bicyclo[2.2.1]heptane
If in a bridged bicycloalkane, the bridgehead carbons are directly bonded to each other, the compound is called a fused bicycloalkane. In other words, in a fused bicycloalkane, the number of carbon atoms in one of the three bridges is zero. eg: decalin
see also spirobicycloalkane