The Collaborative International Dictionary
Omnibus box
omnibus \om"ni*bus\, a. Pertaining to or dealing with a variety of topics at one time; as, omnibus legislation; an omnibus budget bill.
Omnibus bill, a legislative bill which provides for a number of miscellaneous enactments or appropriations.
Omnibus box, a large box in a theater, on a level with the
stage and having communication with it. [Eng.]
--Thackeray.
Wiktionary
omnibus box
n. (context UK dated English) A large box in a theatre, level with the stage and having communication with it.