1A room in which a party is held; a room for hire which can accommodate a large number of people.
2Politics (especially Australian) a room in which the members of a particular political party meet for private discussion, especially to determine party policy.
Origin
Mid 19th century.
Definition of party room in US English:
party room
noun
1A room in which a party is held; a room for hire which can accommodate a large number of people.
2Politics (especially Australian) a room in which the members of a particular political party meet for private discussion, especially to determine party policy.