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 is designed to ensure smooth airflow and structural integrity, either by connecting rocket stages (interstage adapter) or by securing a spacecraft to its uppermost rocket component (payload adapter).