As you’d expect – the battle-space in which advocacy coalitions/policy brokers/entrepreneurs etc slug it out.
See Hilfgartner, S. and Bosk, C. 1988. The Rise and Fall of Social Problems: A Public Arenas Model. American Journal of Sociology , Vol 94, (10, pp. 53-78.
See also venues (sort of) policy monopolies, confluence points
marchudson.net 