The only difference is in terminology (and naturally in territorial applicability, as decrees are only valid in the jurisdiction of the parliament that passed it).
The following five legislative assemblies have the power to pass decrees: This power was introduced in the first state reform in 1970, to the then-established Dutch and French cultural councils, the precursors to the present-day parliaments of the two main communities.
Decrees are not signed and promulgated by the king but instead are promulgated by the executive body, being the community or regional government or, in the case of the Brussels Francophone Parliament, the College of the French Community Commission.
Unlike ordinances, decrees are not subject to judicial review or to supervision by the federal government.
The Constitutional Court is however responsible for supervising the division of power between the federal state, the communities and regions and may annul laws, decrees and ordinances.