Adapter (rocketry)

In rocketry, an adapter is a hollow cylindrical or conical segment between rocket stages or between the top rocket stage and the shroud that houses a spacecraft. They transfer the thrust from the lowest stage and are discarded during staging. It actually link between the first stage of the rocket and the second stage of the rocket. 
This usage, which may appear over-elaborate in that such adapters are inert structural elements rather than dynamic converters of signals or electrical power, actually derives from French.