A constitutional advisory forum for coordination between the Centre and the States, and among the States, on matters of common interest.
Article 263, the Sarkaria Commission origin (1990) and the PM-chaired composition are standard centre-state relations and federalism facts.
The Inter-State Council is set up by Presidential order under Article 263, not directly by the Constitution as a permanent body; it is purely advisory; do not confuse it with the NITI Aayog Governing Council or the Zonal Councils (which are statutory, under the States Reorganisation Act, 1956).
Art 263 advisory body set up in 1990 (on the Sarkaria Commission's advice), chaired by the PM, for Centre-State coordination.