In rocketry, an adapter is a hollow cylindrical or conical segment which provides a sound aerodynamic and structural connection, either between rocket stages (referred to as an interstage adapter) or between a spacecraft and the top rocket stage (referred to as a payload adapter).
An adapter in rocketry serves to provide both aerodynamic and structural support, either connecting rocket stages (interstage adapter) or linking a spacecraft with its uppermost rocket component (payload adapter).