In rocketry, an adapter is a hollow cylindrical[1] or conical segment[2] which provides a sound aerodynamic and structural connection, either between rocket stages (oftern referred to as an interstage) or between a spacecraft and the top rocket stage (referred to as a payload adapter).
It may shroud and protect vulnerable systems such as electrics or machinery of rocket engines/spacecraft from weather or noise caused by running engines.
[3] It is discarded during staging.
Examples of rocket stages featuring an interstage adapter: Examples of rocket stages featuring a payload adapter: This rocketry article is a stub.
You can help Wikipedia by expanding it.