AD HOC stands for "Improvised, impromptu".
AD HOC can als means "For a particular purpose".
Ad hoc is a Latin phrase meaning "for this." It generally signifies a solution designed for a specific problem or task, non-generalizable, and not intended to be able to be adapted to other purposes. Compare A priori.
Ad hoc can also have negative connotations, suggesting a makeshift solution, inadequate planning, or improvised events.