(noun)
the action or instance of collecting people and/or things so that they can be transported somewhere, typically in a vehicle;
e.g. She arranged for an early pickup of the package so that it would be delivered on time.
(noun)
broadly, a device that converts a signal such as vibrations into an electrical signal, especially such a device on a musical instrument like an electric guitar;
e.g. There is something wrong with the pickup of her guitar by which we can't hear what she's playing.
(adjective)
(informal American) spontaneous and unofficial, using people who are available nearby rather than people who have been formally gathered, typically describing a group activity;
e.g. We played a game of pickup volleyball on the beach.