Maryland Code, State Finance and Procurement § 7-217

(a) An officer or unit of the State government may spend money from a special fund or the federal government that is not estimated or included in the State budget or exceeds the estimate in the State budget and is paid into the State Treasury for a program after an approved amendment of a special or federal fund appropriation for the program:

(b) Money that is derived from a source estimated and included in an appropriation act and that is in excess of the estimate shall remain in the General Fund of the State until appropriated by a subsequent appropriation act.