1)
What is "Kol Beis Gadol"?
1.
Rashi: It is Batei Kenesiyos, in which they Megadel (grow) Torah and Tefilah
1
, and the officers' houses.
2.
Radak citing Targum Yonasan: It is every house of a great person.
1
One opinion in Megilah 27a says that it is Batei Kenesiyos, and one says that it is Batei Midrash. (PF)