A type of the council of indra (the king of the gods);
the third council of indra, which is an external one; the members of this council attend the meeting without an invitation of indra.
....bāhiritājāyā.
ye tvanāhūtā apyāgacchanti sā bāhyā.
(Sthā 3.143 Vr Pa 122)
See - Samitā Pariṣad, Caṇḍā Pariṣad.